I think the first recommended approach is the best way to adapt the existing mechanics:
- remove rounds and make it dynamic
- make it so character that has for example 2x more initiative/speed will have turns 2x as often
Wasteland 2 has a system like this, where your action this turn determines how far "down" the initiative order you are pushed.... If you are really fast, and your enemy is slow, you can end up acting twice before they get their next action.
Given that inxile and Obsidian are now both part of Microsoft, perhaps inxile could send over some design docs / specs... or catch up on a call to chat it through?
I hope that doesn't sound snarky, because I really like the output of both developers, and if they can actually share advice / learning, we all end up much better off!