Comment 6 for bug 485687

Upgradability means that if you solve another problem, you can easily deploy a fix wherever you need it, instead of having to rely on the fix being solved upstream.

However, I can see another interesting issue wrt SBCL distributing the new ASDF2, which with the current SBCL ASDF hack would shadow any ASDF upgrade you'd like to distribute to replace it. So you couldn't asdf:load-system :asdf, you'd have to load the new asdf.lisp. Same situation as ECL above, except the bug would persist from new to newer ASDF.

Shouldn't be a big deal. But hopefully we'll find a better way.