A few things about playing and then returning cards to the research mat:
How do you intend it to work with durations and reserves? After your turn, and Anthropologist leaves play to go into the discard pile, a duration cannot really leave play; Hireling becomes pointless, and where will cards with a Haven, Gear or Archive go? Reserves themselves leave play, would they move from the tavern to the research mat?
I would suggest 'treat this as a card on your research mat' instead, but I notice you can actually get a selection of cards of the same price, if you have two Anthropologists in a turn, the first takes a card off the research mat to play it so the second can get a card the same cost as the one just played. Unless you keep the ramp-up idea set so you only have one card per price tier, I guess you're adding a lot more words to qualify all cards correctly, something like 'when it would be discarded at Clean-up, return it to the research mat.'