I think changing the point buy would go a long way. Instead of 27 Point Buy and +1/+2, which is a redundant mechanic, give 44 Point Buy for Story, 36 Point Buy for Balanced (resulting in the same min/max as if you used the +1/+2), and 28 Point Buy (with no +1/+2, resulting in lower attributes than you currently get) for Tactician as a baseline (in all cases, a 16 or 17 would cost 3 Points and an 18 would cost 4 Points). For those who want something harder or easier, you could also allow decreased or increased Point Buy from baseline. Some people were complaining the game was too hard on Story Mode, so allowing them to have a 44 Point Buy would probably go a long way to making that issue go away, with the option a 60 Point Buy to make it really easy (I don't think you need an all-18 option because that is kind of boring, but it isn't much coding work to let the Point Buy slider go all the way to 114, or "all 18s"). While at it, you may as well let players adjust their attributes down to 3 and allow them to start with, say, 0 Point Buy, which I think would be a real challenge on Tactician.
I don't think all of this should be pushed onto DLC because it is so easy to just code in adjustable Point Buy. And if you put it on the "Difficulty" screen, there will be no confusion about whether you are making the game easier or harder than the difficulty the game designers thought was about right.
You could also handle the Point Buy change with a toggle that allows you to either stick to the appropriate points or "break the rules" and just get a warning when you venture forth, such as "Your character has higher/lower point value in attributes than is recommended for your selected Difficulty. Venture Forth anyway?" The advantage of that is you can roll attributes and then just plug them in, ignoring the usual point buy limitation, especially if Larian reduces the floor for attributes to 3 and increases the cap to 18. It would also be easier to understand for new players if you had a toggle on the Difficulty Screen that was essentially "Allow attributes to be higher or lower than recommended?," especially if attributes was hypertext, than a question about Point Buy, which is a more abstract concept.
