Frankly, I don't care that the dev isn't very loud on the internet, and a new build every 6 months seems perfectly fine. And if it stops being developed, it's a standalone app, it will be many years before it bit-rots. I will be using it for years whatever happens.
But if it were open source, people would know that if it ever got dropped it other people could keep it going longer.
I'm really only concerned with it bit-rotting though. New features? Who cares? It does everything I want it to and I was already using third party syntax definitions to keep up with language changes, it's not like it matters if Sublime doesn't change much. It looks like they'll have high DPI support complete soon if not already, so once that's done I'm really struggling to think what else I want out of it. Not that I have a high DPI monitor, but if we're thinking about things that might make it unusable in the future if it gets dropped.