i am happy to see jon is responding. welcome back jon! and i hope that you won't disappear on the future, i think it is better to hear bad news than not hearing anything at all.
regarding the issue you have raised. i have a different opinion. i want to question the need for another UI. lets begin with the facts, at the moment the sublime editor is the best editor around for windows, the implemented features works great and it is delight to work with. i found my self switching from using different editors to work only with sublime. the current half implemented project management is already very good and it is more than many other editors offer. regarding the tab problems, how many times a day you need to do that? yes, i guess we all tried to drag a tab between windows (like google chrome) but it is not supported. so what? i only need a descent text editor, not a tabbed browser. regarding the last issue, the h/w dependency and the ability to work under VM, again, ok, nice feature, but is it the killer feature that we can't leave without? i will say it again, i only need a decent text editor.
text editor most important features imo are the possibility to do things faster and with ease: automation; easy plugins; good community which produce extensions; stability; speed.
i will sum it up, why make the next generation UI a 'live or die' decision? i am better off with a living sublime with the cons it has. jon, maybe you have aimed the wrong target? there is no perfect product, you can plan one, but the implementation time will eventually make you choose what really important and what's not. what is a must and what's not.
that's my humble opinion.
let me be clear, i am not against a better UI which solves all the things jon mentioned, but if i understand correctly, jon feels it is not a trivial work at all, which can take a lot of time, and may even cause him to abandon the project out of frustration. if that's the case i say: stop walking on this path, it is not worth it. keep your objectives reachable, let the next guy fix the world