Although I wish they’d explore the Kakoune/Helix style of editing too, which I think will become a major competitor to Vim (and I personally prefer it myself).
However, I am also worried that Lem won’t gain any traction because the Emacs ecosystem is just too vast and has too many killer apps (Magit, OrgMode, Dired, the amazing built-in Help/Documentation - to name a few).
But it may very well become a modern Emacs alternative if they focus on better user experience, leave behind some idiosyncrasies of the past and create great alternatives or ports of Emacs’s most appreciated plugins. There is a great opportunity in starting from scratch, but I guess it is also a huge challenge to compete against decades of development, a huge community and a rich ecosystem.