Apologies for not having fully internalized your post before responding -- you make a good point that there's functionality for which we need real, unrestricted evaluation.
Whether that functionality is worthwhile is a different matter -- my immediate use case is one where I care about extracting accurate-as-possible data for a large number of packages *quickly*, and I'm actually somewhat unhappy with how expensive the current approach taken by makepkg is (considerably more subprocesses there than could be strictly needed if we streamlined it).