> We wait for a new version too long this year:)
I have a good experience with compiling and using emacs-NextRelNr branches. Since at least emacs-25 (~4 years). I made myself a fish-shell script
https://github.com/Bost/dotfiles/blob/master/fish/functions/make-emacs.fish to compile the code and git-tag it, if there's a change in the code files since my last compilation. (The script doesn't proceed with compilation if only documentation changed.) I tag the repo just in case something's broken, so I can just checkout the previous tag and rerun my script. (The script is not 100% maintenance-free, but I don't bother editing it now and then.)
I use spacemacs (daily), mostly for clojure development. And I update spacemacs, plus installed packages almost daily. Everything works fine and I don't encounter any problems more than once a year, including problems with packages.
The only problem I have is with freezes when editing larger files (> ~1MB) especially with long lines. But that's a general and long standing issue. In such a case I just `killall emacs` and try to run `emacs --no-init-file`. It helps in about 50% of the situations.