A good question, well asked!
There was a point when we were told that "Blasma" was just around the corner. The date for that seems to have receded and there are now no promises.
As a heavily committed user I find it worrying that there is no visible means of support for Nabble. They are no fees, nor is it currently advertising supported, nor does it promote itself as an open source project with a group of dedicated volunteers behind it.
I used to have a post on my GregHelp site that used to have links to a number of statements found on Nabble Support that reported on Nabble's future but that seems to have gone missing! :-(
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.