One site per system looks like it will quickly pollute the host namespace. What about we instead use a single logical host with subdirectories?
#P"COMMON-LISP:SYSTEMS;CL-PPCRE;CL-PPCRE.ASD"
The problem I have with this approach with logical pathnames at all is that I don't understand whether or not mixed case and other characters are allowed at all. They clearly aren't portably printable if they're allowed, but I suppose that's an OK limitation. In any case, if logical pathnames with names including mixed cases, dots, dashes and underscores are not allowed at all, or there's at least one supported implementation that will bork, I think it's a non-starter.
On the other hand, maybe it's time to have make an amendment to the CL standard that will make LOGICAL-PATHNAMEs usable at long last.
[ François-René ÐVB Rideau | Reflection&Cybernethics | http://fare.tunes.org ] Faith, n: That quality which enables us to believe what we know to be untrue.