I work in LEM for my personal projects, that dont have other LSP integration needs and hooks into my org-mode/org-babel workflow. These should not be show stoppers, but will eventually be a non issue.
There are however some features that I'm missing in LEM before I can fully switch over.
1. The documentation for Lem is lacking. 2. I have lazy hands and hit shift on some keys when I shouldn't (shift and backspace for example). I'd need some way to ignore that. 3. An built in undo, (c-x u equivalent). 4. A documented library interface (this is kinda #1 again)
I will eventually get around to making my own plugins to solve most of these. Its a matter of time vs tradeoff.
Download micros, put it in your local-projects
git clone https://github.com/lem-project/micros
Load it.and run.
(micros:create-server :port 50000 :dont-close t)
Then use m-x slime-connect in lem.
It is not slime, but it works.