How I imagine leveling on pristine realms will go is they'll look a lot like the regular PVE/PVP realms. There will be super active 1-10 and 10-20 zones, then every zone from there on after will become more and more sparsely populated until you get to the point where you're the only person questing in a zone. In regular servers that's just because a lot of people just spam dungeon and battleground queues, while the pristine realm higher level zones will just be dead at that point.
Who knows, maybe people will come back for pristine realms, maybe some tight knit guilds will come out of those early questing and dungeon groups, maybe zones like Un'Goro Crater or Outland's Nagrand will be super-active but it just seems so unlikely.
I'm more keen to see Legion's flex-leveling applied to the whole game, then you could play a zone from start to finish and get decent exp out of it, or maybe you could start in any expansion you wanted. It would be awesome to finish a starter zone and just go play MoP or Cata instead of grinding the same starter zones in 1-60 Azeroth over and over.
Dunno, servers crapping themselves randomly out sounds like Vanilla WoW to me.
Oh but it wasn't random, it just required lots people killing mobs and getting a specific item, the new f2p currency, to drop. The more it happened, the more bogged down the server would get until the game became unplayable and the server would have to restart. It happened like clockwork, every few hours the servers (all two of them, one PVE, one PVP) would get taken down for maintenance. They basically didn't do a large enough, staggered stress test. They had more people hammer on their servers during the f2p re-launch than they did when it was sub-based, not necessarily a bad problem, and they introduced new issues with some of their f2p currency system. You would come home from work and try to log in just to be met with an incredibly laggy game if the servers weren't down maintenance or you weren't stuck in a queue waiting to see if the game was a laggy mess when you could log-in.
They did add extra mega-servers but the issues persisted and what people may have had patience in 2004 with WoW, they sure as shit didn't in 2015 with Wildstar. After two or three months the population began to drop off and recently NCSoft laid off half of Carbine's staff with the other shoe expected to drop for the remaining staff soon. Probably depends on how well the re-re-launch goes on Steam.