just occurred to me the only game that had this was red alert 2.
this was done with spies originally but perhaps it could be done another way if not for spies.
also the ability to build your units promoted from the factory (tho i thought that was done better in emperor battle for dune, Atreides could send in infantry that were promoted into the barracks to do it)
if you capture any enemy building you can build the enemies stuff so why not be able to make some mixed tech stuff by research and capture?
say you would need to have a tech center and do some research as well as the specific enemy stuff to build it.
depending on what you capture depends on what you can build
in a way the gla technically do it already in generals 1 with there scavenging of destroyed units