Details has an interface that allows you to see the talents of other players if they also have Details installed. It would be nice if you could hook into this (if it's publicly accessible) to detect if someone is in healer spec.

If you added automatic detection, you would also need a way to manually include/exclude people in case they're healing while in a different spec, or not healing while in a healing spec.

Currently i don't know about hooking the data from Details, this would indeed be nice if possible.

There is a current plan to have a similar effect implemented: But instead of just going by specs it does look for specific buffs (shadow form for priest etc) to skip them from the overall calculations.
Sadly this doesn't cover all classes as far as I'm aware