There is a priority pass lounge under construction in LHR T2; so hopefully someone can report on it lager this summer :-)
First impressions of T2: certainly feels more spacious than T3. Bag drop not opening until 0545 is not mentioned anywhere and lots of pax in wrong lines (bag drop instead of check in) and seemingly getting incorrect info from "welcomer" staff. The *A (contract?) Staff that were correcting people had plenty of work to do and their empathy was definitely being tested!
It would have been a smart move for the first lounges to open to have had some kind of reciprocal access while the terminal is just starting to open. It is definitely not at full capacity so I doubt the UA/AC lounges would have been at bursting point. Of course, the chances of that would have been near zero but a good PR move all round..