Personally I'm not keen on a recurring payment unless there's a clear benefit. For an editor, that'd be having a team committed to making it better. The JetBrain guys have shown good progress.
What I would pay for would be an editor in the style of ST2 but with a few IDE features like being able to jump to method definitions by shift clicking etc.
Basically a very lightweight IDE with good text editing features (like VIM style keyboard shortcuts). Integrate a terminal into it, but do it in a very slick way with the ability to run "recipe" type commands.
For example if I forget the switches for a git command, I should be able to search for roughly what I want and have a result return which will populate a command in the terminal.
This might mean hyper focusing on a few languages however.
Not sure I would like the recurring model for just using the editor. Since this would likely mean you would have to implement some sort of always on cloud integration into the editor which would annoy me and make me worry about losing access to my editor.
What I might pay for on a recurring basis would be access to a repo of high quality plugins that were well integration with every version of the editor. Also maybe some functionality to allow me to share the editor session with someone remotely.
It would be extremely annoying for that to happen because a payment got screwed up or something.
If you make an editor so good that everyone wants to use it you can probably make enough from one off sales assuming you set the price right.
By and large when it comes to tools I want to buy them and keep them rather than lease them.
If development started to get stagnant I would probably "forget" to renew it after my CC expired or something like that. Or at some point I'd just feel "I've given this guy enough money" and cancel even if I kept using the editor.
There are a lot of things that would be nice to see in existing programs that a bounty type system would possibly work well to encourage.
a) Fast startup times
b) Effective utilization of multiple monitors out of the box
c) Embedded prompt for dynamic languages
d) Minimal lag in the UI
e) Fast regex search over multiple files
f) Multi file mode - I want to be able to have multiple files mapped to the same buffer and have the ability to quicky seek to files
g) Outline mode that is code aware
h) Integrated lint mode
i) < 10 meg download size
All of the above in the same editor. Currently sublime comes the closest, I have also happily used emacs in the past but sublime feels snappier than emacs currently. I guess if emacs could be as snappy and pretty as sublime what it would scratch all my needs, because modulo some polish it has most of the other features.