At last I can post in the US too (EU player here)!
I’m very interested in the population matters, and overall according to raider io, which seems to be the most reliable population tracker atm short of actually playing on these realms and doing A LOT of who checks, they’re all typical mergers, taking low or medium realms and making them high pops, exception made for garona + icecrown and malygos, which are a little lower than the others, and garrosh + aegwynn and the rest, I’m pretty sure the 2nd of these clusters has to be high pop, this is something blizzard occasionally did or tried to do in the past.
For example back in 2013 or 2014 in the first round of connections, they connected the low pop dentarg EU to tarren mill EU, which was high if not even full, and nowadays if I check a single zone on who I find 49 people from tarren mill, 1 from dentarg!
They tried again in russia with razuvius + galakrond recently, low + high, but connection failed, and then again in germany with mal’ganis (low) + blackhand (full) but failed again.
As far as I know, these kind of aggressive connections were much rarer in US than EU, cause if I go check population sides your biggest connected realms so far are way smaller than the biggest servers, while in EU you will see connected realms much closer to the top.
As for the ones who complained about rares, it’s a logical reaction, I had it too at first, but actually the rare hunt will not be impacted significantly, cause there are cross realm zones active.
If you are on a normal realm that we will call A and A gets connected to B and C, you will not have a harder time finding rares than before, cause even atm A, B, C, D, E, F, G, H, I, J are in the same cross realm zone, all this does is make the range of players you can raid, trade, AH, guild with wider.
The only time where rares will be significantly impacted is if you clearly see they’re connecting you with a realm group that is in a different crz than you currently play on, but as far as I know blizzard tends to not do that.