G'day Alain!
I realize (from reading your sources so far) that you're focussing on CMUCL and SBCL; however, if the intent is to try to make the protocol sufficiently general/portable to other Lisps, I hereby volunteer my services as Lispworks user/tester/debugger (and even, initially) porter of whatever LW specific code needs to be written to get SLIME going on LW.
Great! The OpenMCL backend is currently the shortest/simplest, so I would guess the easiest approach it to port that to LispWorks.
If you write that, we can run the test suite against LispWorks along with the other backends. That way we can avoid breaking it during restructurings. I just installed LispWorks Personal Edition for Linux, which was painless, so I think this will work.
As you've probably noticed, we're just taking the first steps in creating a sane way to interface the backend-specific code with the common stuff, so everything will change a fair bit in the coming weeks. That said, personally I would be happy to have a LispWorks backend in any time -- I don't think it will be much extra work to maintain, and it would be good to support it.
And we may even trick you into writing some code that benefits the other backends too. :-)
Cheers, Luke