However, we should recommend against using lists this way, for two main reasons:
Lists have surprising behavior in nix-build. Being able to put them in an attrset seems like a reasonable expectation, but there's no way to make that build in nix-build.
Subjectively, an expression returning a list is a dead end. Taking elements out of a list can be done, but is error prone. The only 'good' way to use a list of derivations is to use all of them at once, like in buildInputs.