Adding some of my thoughts on things that could be done with the Emperor's storyline, kinda related to the idea of seeing a fully developed "distrust" path.
I feel like the Emperor needs to have the option to be more evil towards the party. Many remarks in the game, particularly from characters like Raphael, make it sound like we're being used and abused by the Emperor. But in the actual gameplay... he might raise his voice a little, but he can never DO anything to your party -- except in the case where he almost refuses to accept Minsc into the party. That moment was one that really stuck with me, as I thought I was finally seeing a glimpse of the conflict that was going to lead to me fighting him in the end, although nothing else supported that. (I was genuinely surprised when I chose to accept Raphael's deal, then tried to hide it from the Emperor, then let myself fail, and then he... still couldn't do a damn thing in retaliation. I was really expecting to see the consequences of antagonizing the mindflayer that holds our lives in his hands there).
I'd like to see more cases of the Emperor being able to more actively interfere with, argue with, or even harm the party, if the party is hostile towards him or fails to negotiate with him. For example, throughout the game, allowing the Dream Visitor / Emperor to psychically manipulate NPCs to avoid answering questions that may be inconvenient for the Emperor, rather than just complaining when the player pursues these paths. After revealing himself, particularly during the first fight with the githyanki, I feel like arguing or questioning him should have the potential to have the Emperor just temporarily mind control the party into defending him, since the game forces you to assist him anyway. Carrying on with this, I feel like the Emperor could be seen arguing with party members in camp scenes (like the old Lae'zel vs Shadowheart) and possibly threaten to expel him from his protection unless they submit to him. These sorts of encounters are mainly meant to cause friction with the player and make them "feel" the control and manipulation the game seems to think we should be feeling; actually losing a character to these encounters should ideally be rare, although the consequence might be upsetting your other companion by having to cave in to what the Emperor says, thus building a sense of "We need to get rid of this guy" among the party. For less hostile versions, the party members could be trying to demand help from the Emperor, which he is refusing (as in the Minsc case), and persuading him to help would improve relations all around.
For some examples of the Emperor interfering in the Orphic Hammer questline:
- If the Emperor knows that Raphael offered the party the hammer, and he notices the party attempting to enter the hells to steal it, then he can put two and two together and tries to interfere. If the party fails to persuade him to allow this, then they must resist his attempts to control them and destroy the ritual circle. If he succeeds, they cannot enter the House of Hope but can still bargain with Raphael. If he did not know of their intentions prior to them returning with the hammer, then he will voice his disapproval but will not act at this time.
- After retrieving the Orphic Hammer, if the Emperor has not been persuaded to allow this, a camp event can trigger where you wake to find Lae'zel (if available) wrestling with an NPC who's trying to make off with the hammer. The NPC is being controlled by the Emperor and was going to try to hide / throw away the hammer to prevent the party from using it. The party can possibly make a deal to allow the Emperor himself to keep the hammer if they're trying to convince him it's just a tool they want to have in case of emergencies (in which case, it'll be in the astral prism with him until the finale). He probably can't succeed in throwing it away, regardless; the camp is too alert, and he'll realize this was a futile effort.
For a "trust" path, in addition to the Emperor's own little quest (which I think needs to be reworked a little), there should be ways to convince the Emperor to be more cooperative, via diplomacy checks. Basically, a mix of showing him empathy and also appealing to his logical thinking (i.e. knowing how to argue that things are actually in his long-term best interest) and convincing him that actual trust, rather than controlling everyone around him, is valuable. If enough interactions with him are resolved this way, he'd be more receptive to the player's later proposal to negotiate with Orpheus, and far less inclined to betray the player in the end.
For the "distrust" path, if the player is either always forced to begrudgingly listen to the Emperor, or only persuades him via threats / intimidation, the Emperor will be very unlikely to negotiate with Orpheus, this route may even involve him ultimately betraying the player and taking control of the Netherbrain in the end (assuming they didn't kill him and side with Orpheus). This is the result of reinforcing his mindset that he must control the party for his own survival.
I feel like his personal quest needs a bit more of a proper resolution / choice than simply exploring his basement. Something a little more like what we see with Astarion, or even similar to Gale, where there's a sense that there is a choice that this character will be making, and what is done here will be a major factor in how it resolves. Personally, I thought investigating the truth about Duke Stelmane's connection to the plot and the Emperor was going to lead to something of the sort, but that isn't how it went. That is, rather than just concluding that she was on a list of random murder targets, I thought we'd be learning about what she and the Emperor were up to that led to his capture, with some unresolved threads for him to act on. There's flavor text in books related to that, but they had no bearing on the actual storyline.
Edit: For some other changes I would make to the finale:
I don't think that the Netherbrain should immediately turn all its infected into mindflayers, especially not the ones within the city. This means that, similar to the Gale Act 2 ending option, there are a number of "hostages" that are infected but can still be saved.
Then, if you side with Orpheus and kill the Emperor, I don't think it should be required that anyone turn into a mindflayer. Instead, I think that the result should be that Orpheus and his warriors can help you kill the Netherbrain -- but those who were infected will turn (except the party themselves, due to Orpheus's protection or the netherstones or w/e). This matches with how Orpheus expresses that the party were already a lost cause and should have allowed themselves to be killed by his honor guard; he doesn't see the infected as able to be saved. And in this case, I think that if you still want to save the infected, you will have to convince ORPHEUS to that you can be trusted to turn into a mindflayer and take control of the brain without betraying him. Probably some hard skill checks, otherwise he rejects this notion and will not let you transform (locking you into the "kill the brain but lose the infected" route). Orpheus himself will not turn under any circumstances.
If you side with the Emperor, he is able to take control of the brain, and as in the current good ending, he can free the infected. The catch being that with the trust/distrust branches in the Emperor's storyline, he'll only make good on this if you've been building a good alliance with him up until now. Otherwise, he just takes control of everyone for himself. If you turned into a mindflayer and demanded to keep the netherstones, you can still fight him for control in the end.
The option to get both Orpheus and the Emperor working together is a mix of both "good" endings -- Orpheus agrees to trust a mindflayer to save the infected, and the Emperor follows through on his part of the deal, sparing the player character from having to turn into a mindflayer unless they just felt like it for some reason.
