From a few players and a couple of posts I have seen here, their is a general concensus that this is a low pop server, the exact opposite is true. Right now as a combined realm it is in fact one of the largest NA servers #15, as far as US based severs and excluding RP it is ranked #10.
To put it into perspective I am rerolling from a server that has 3 horde guilds doing progression raiding here their are, at last look, about 50 horde guilds doing progression when i looked in the first week of the new raid tier.
Currently the server is the largest players can join and blizzard is funneling new players to the realms on the server as they did to Dalaran last year. That means many new players and players, like me, rerolling to the server as it is likely to be locked once it is sufficiently filled.