Fontconfig can give you a lot of information about installed fonts. Unfortunately that requires installation in the first place and does not help people that just want to check the capabilities of a set of font files before installing them.

To take an analogy, rpm has a query flag that will work on all the installed package base, but you can also ask it to examine a set of uninstalled packages using the -p flag (rpm -q -p /tmp/foo*rpm)

Please enhance fontconfig utilities so it is possible to make them introspect a set of on-disk font files instead of working on the fonts installed on the system.