While I really hope Tromey's effort succeeds, I really think that this is probably a different effort with different goals. Porting Emacs to CL would greatly strengthen the platform Emacs is written on and would add a lot of features for free. Porting Emacs to the JVM, however, might also provide that, but would also provide simple access to the Java ecosystem, which would be a substantial boon.
There is an "emacs" written in pure CL - LispWorks - yes it's commercial, and not exactly the same as emacs - but very close. Some versions of LispWorks comes with the whole source of the editor, and the environment.