Hard question, it really depends on my goal, for building a quick prototype, I'd certainly use Etherpad again because it is trivial to launch it, and, more or less, it has worked reliably for the last years. On the other hand, collaborative editors have lots of progress with CRDTs now, it is worth re-evaluating options.
I'd bet that the key would be whether Etherpad can be easily customized to fit your goal.
Of course, as a dev, I was fantasizing about potentially writing my own collaborative editor someday if there was a way to make the project financially viable , for sure, this is the least important thing to make it get there.
> Did you get requests to support non-Etherpad servers?
Not really, I think I have got less than 5 emails about this project so far.
> I'm thinking of adding text collaboration to an open-source project I maintain
If you don't mind sharing, what's that project about?