Pausing the whole world really isn't needed, though, is it?
Would it not be better to work within the framework they have (radius pausing on beginning of combat) to expect an actual change to get implemented. With that in mind, only a few changes are really needed:
1) Increase the radius of actors that would pull things into active initiative rolls for combat (300ft?).
2) If you perform any action that directly affects or indirectly affects anyone or anything within the radius of any actor, you roll for active initiative for that combat and is paused before said action is performed.
2a) If your initiative roll is higher or equal to the current initiative, you are placed next in turn, as you have not had your turn yet (no skipping a turn of combat). You still maintain the initiative you rolled, meaning if you rolled a 19 and current combat was at 12, you will act next (Dex to break ties) but the next round of initiative, you will get your turn as normal (at 19).
3) Anyone who has failed to see an actor but is within an actors radius range is still pulled into initiative combat but can't act/see the particular actor/actors (AI can't make decisions on those it can't see/players just don't see the AI who they failed to detect).
3a) If two actors fail to detect each other and are within radius range, but others within radius range do not have initiative, then no initiative is forced upon you.
Basically, if the radius around an actor is 300ft and if that is within range of anyone that has initiative going, you will automatically have to roll for initiative and proceed as turn based. If you perform an action that is targeting in some way within another actor radius that has initiative, you will be pulled into initiative (think of you are 470ft away and you cast fireball at the ground 320ft away from an actor but the area of effect is 20ft, that area of effect is within 300ft of an actor with initiative and will cancel your action and roll for initiative).
This still allows for players to be 301ft away from any actor in initiative, cast buff spells on you quickly while the other actors might be able to just sit there doing nothing, but as soon as you get 300ft away, you will be pulled into combat, and 300ft would take you several turns to get into range.
This also fixes the stealth issues in that if you are stealth and no AI enemies can see you but you are within 300ft of a friendly person who is in initiative, you will automatically go into initiative. If you are the only one stealth and nobody else within 300ft is in initiative, you can proceed as normal until an action is performed (anything other than movement). As soon as you perform an action, you and everyone else with 300ft of you are pulled into initiative, along with everyone else who is pulled in, they will pull in those within 300ft. Think of it like a chain reaction, checking, pulling in those who are pulled in each time, until all actors have been checked and nobody else gets pulled in. This should resolve any/all stealth combat weirdness that is happening right now.
The rolling of initiative and coming into combat mid way, you will not lose your turn, but actually would have acted like you delayed your initiative to the current initiative (if you rolled equal or higher) or will proceed as normal if rolled lower than the current initiative. This keeps people from not losing their turn if they were to come in later. Of course, coming into combat will guarantee you are at least 300ft away, making you take several turns to get in to range to do something.
At least, this is how I view would resolve their problems that I see off hand in the few play throughs I have done.
