Something like Lem[1][2] could go even further because of the richer CommonLisp ecosystem compared to Elisp one.

[1] https://lem-project.github.io/

[2] https://github.com/lem-project/lem

I chose the JS ecosystem. Why does the power of Emacs not belong in the browser? These days JS is a powerful enough FP language to do it.

Having CommonLisp as the extension language would indeed be a great improvement over Elisp.

However, I am suspicious about the dependency of Lem on Webkit, which for me is rather associated with inefficiency and low performance than with the instant reactions that I expect from programming text editors, terminal emulators and tiled window managers.

The main problem is that it is very difficult for any replacement of Emacs to offer everything that already exists for Emacs.

In my opinion, the only way in which such a replacement would succeed would be if it would include an automatic translator from Elisp to CommonLisp scripts executable by it, with equivalent functionality.

I am not sure if I would bet one way or another on who has the richer ecosystem here.. They are both great. I would probably wager elpa has more packages in general than quicklisp, but maybe not necessarily richer/higher quality.