> Consider the poor quality of the existing js modes for 26.x, any idea why this depends on a future version of Emacs instead of current versions?

You might as well look at the thread js2-mode was revoked[0] and ergoemacs' article[1].

> Alternatively, could somebody convince the author of the railwaycat port (Emacs with better macOS integration) to get a version 27 out soon?

Er... I would like to point out that it's not 'railwaycat' port but more of Mitsuharu Yamamoto's port[2], and AFAIK he has claimed that he has no interest in maintaing an emacs27 version.

[0] https://lists.gnu.org/archive/html/emacs-devel/2009-08/msg00... [1] http://ergoemacs.org/misc/emacs_javascript_mode_war.html [2] https://bitbucket.org/mituharu/emacs-mac