I've read this argument multiple times and I just don't get it. Is it because you were waiting for a feature that hasn't been implemented? What's a decent release cycle? How does a indecent release cycle affect your daily usage of the text editor?
If that subset is large enough such a migration can harm the ecosystem: less users, less developer mindshare in bugfixing or plugin development and so on. It can then work like a run on the banks where people get out before the problem gets worse, making the problem worse.
Interestingly, vim is often one of those editors: when TextMate was originally dying (pre open-sourcing) there seemed to be a new "why I'm switching to vim" or "how to set up rails dev in vim" post every day. I'd wager that a lot of people moved to vim as a result, then bounced off again.
I stick with ST because the plugin ecosystem is vibrant, it's hackable in a language I'd actually want to write, there's as much time-saving juice as Vim without me having to learn non-standard keyboard commands for the very basics (sorry, I like my arrow keys and Ctrl+x/c/v, and - god help me - my mouse), and it's not a sluggish, half-complete rip off of itself (cough Atom). I know enough Vim to get around a log or config file, but for serious work, Sublime and my brain are partners for life. (Unless Atom improves dramatically, anyway.)
I don't suffer from the slow development cycle, but I'm sure others do, depending on what it is they need.
As for open sourcing it: if you have barely enough time to work on a codebase yourself, it seems unlikely that becoming the co-ordinator of an open source project is a reduction in the amount of effort you have to make. And poorly-run open source projects don't generally have a fast release cycle.
It is not that the editor is in bad shape. The periods of of inactivity made me feel like the editor could be abandoned or discontinued. I went back to Emacs.
You do know that there can be like decades between major Vim releases, right?