The thing is - cross realm zones aren't really what's needed, if anything in WoW you want as few peeps in a zone as possible to reduce competition for mobs and resources (particularly since most/all elite mobs/group quests are now gone and shared tagging of mobs is still few and far between). What you need is a good population to support crafting and trading - and a decent city based population to allow pugs to form (exactly the opposite of what cross-realm functionality is bringing).
Back in TBC waiting times to get on our realm (Hellscream Europe) were anything from 15-40 mins at peak times - I'd happily accept that tbh. I'm sure those on realms that waited 2 hours plus wouldn't and that's fair enough - but that's what balancing the population is about. Of course they could develop something akin to GW2's overflow servers which are working very well indeed. Heck they'd probably have enough server capacity left over from shutting down the underpopulated realms to not require any new hardware - just reconfiguration of the existing architecture. But I guess their dev team is now so small that such a grand project is just out of the realms of possibility, sigh.