I'm considering making a 70 twink right now. First let me say the current days of twinking aren't what they used to be where level 19 rogues and hunters roamed the BGs looking for juicy 163hp targets in whites and greys.
You can turn off XP to fight other twinks now, and with the BG merge this is viable (especially if you play the underplayed side, ie: Alliance). Queues are pretty fast and you're only matched up against others who turned their XP off as well. So really, you don't have to feel guilty anymore about picking on undergeared targets. Everyone who turns their XP off WANTS to be there.
Why level 70? Well I was looking at the Brutal Glad vendor in Area 52 and gear is CHEAP! I'm talking brutal glad 2h weapons, 350 honor. Every piece from the 5 set is 175 honor or less (chests, helms, etc). They even have DK gear which surprised me (I have a 71dk).
I'm probably making a 70 resto shaman. And my 71dk who I'm leveling will pick up osme of the gear and stay in the "XP on" bracket.
Only problem is right now theres no Guardian gear vendor, but I hear the vendor is back on the PTR and all Guardian off-set pieces are less then 100 honor. So extremely viable to gear up quick for less then 2k honor. Seems fun to me. In the XP on bracket you see a ton of people in brutal gear since its dirt cheap. If you PVP at all while leveling you can probably buy a bunch the second you hit 70.
I have nothing against 85 PVP but I only have time to keep up with 1, maybe 2 characters. Its nice to have some 0 maintenance characters in lower brackets who are geared and dont need "maintenance" ie: honor/arena grinding every season. Sometimes I just want a different playstyle.