I haven't added the slots yet, so of course it won't work. As for disabling properties on old versions of ASDF that don't actually support them, that's what #+asdf3 is for, just like #+asdf2 before it.
When it is time to add support for a bug-tracker-url slot, will there be a feature for that? Or will that be done via subclassing?
Now is a good time to request such features, before ASDF 3 is actually released. After it is released, and until another major release follows, subclassing will be the recommended way.
—♯ƒ • François-René ÐVB Rideau •Reflection&Cybernethics• http://fare.tunes.org The politicians have a most touching faith in technology — that it can make up for any dumb thing the politicians decide to do. — John McCarthy