Hi!
I find the USE flags system that Gentoo uses quite inspiring.
I don't know whether this can sensibly be simulated through *features*. On one hand, you get the conditional compilation for free, on the other, *features* to me seems to be intended to represent features that are present, not those that you'd like to be present.
I guess that a proper implementation of this requires an extension of both ASDF and Quicklisp.
Gruß
Svante