No fully obsolete researches.

[ErissN6]

Maybe, for the pleasure of gameplay, there should be no research to be totally obsolete.

Maybe give a very tiny advantage for each of those to-be-obsolete reasearches, like rifle researches giving differents +1% damage on all rifles vs something, with armor researches giving differents +1% protection on all armored units vs something, etc.
So, it could too make those old researches usefull in the end of game, like all other researches...