Alright, I've packaged it as you suggested.  See the wip-nextbrowser branch.
If was slightly simpler as for Sly.

That said, I wonder if this is not over-complicated.
Wouldn't it be easier to mimic Quicklisp there and automatically push all .asd
to the central registry?  Or make the central registry configurable, so that
packages can decide what goes in there?
That would replace all those "define"s with a single line I think.

Thoughts?

-- 
Pierre Neidhardt
https://ambrevar.xyz/