[6AA4FD]

This is probably because it is relatively easy to add more elisp flourishes, another seven major modes for editing JavaScript, much harder to actually improve the core.

[shadowgovt]

As with any large system, improvements to core also risk compromising large, popular packages.

[agumonkey]

I wonder how remacs guys are doing now

[the-smug-one]

They're no longer taking PRs, development has moved over to emacs-ng with a different perspective on how to improve Emacs.