1) Improve the default theme: Maybe set a default dark theme to make
emacs feel more modern. Experienced users usually already have a custom
theme, so they won't be affected. There is actually some statistics
about downloades themes here:
This would be an utterly disastrous change. As an experienced user, I
do not have a custom theme, and prefer to use the defaults of Emacs.
Same for me, and I'm pretty sure we're not alone.
Also, while dark background is popular right now, it's not necessarily better. Apart from the fact that there is actual science showing that dark backgrounds are worse for one's eyes, I believe the current trend is merely the pendulum is swinging back.
Recall that backgrounds used to be dark back in the terminal era. Then monitors became better and white background was finally usable. Now, people who only ever have experienced white backgrounds wants to change things for the sake of change, so that is now popular, even though it's actually quantifiably worse.