No. More Room Through Coach, the AA program, was fleet-wide, and not something you could purchase separately.

Given that it's international-only AND is going to require 75K+ miles to get for free on DL, I think it's still an open question if E+ will be retained fleetwide on UA in it's current format- though I suspect it makes DL's move makes it very likely that E+ will be retained in some capacity on longhaul.

That being said, I am because DL's A330s were at 33" pitch in the front rows, and it's a lead-pipe cinch that is going away... and you only needed DL Silver (or partner elite) status to get one of those seats gratis.