What some people should consider is that there are typically near equal amounts of horde and alliance queuing up. Horde has been more popular in the past, but regardless I'll show you how this won't have much of an impact on things.
If exp on and off were merged, we would see many games popping very frequently with maybe only around 2-4 twinks per game on both factions. Sure that means there's a lot of "dead weight" for those looking for competitive games, but outside of wargames and premades, that's not necessarily a bad thing as those games will probably be quite competitive. Annoying, but competitive. It would be like a 4v4 wsg with obstacles and annoyances to create challenge in those 4 players.
What if one faction gets 5 twinks and the other gets 2 twinks? Those 2 twinks will have to coordinate with their 8 other teammates if they want to win. This isn't necessarily a bad thing either as this is educating non twinks and challenging twinks alike.
Twinks currently are not that much more powerful than nontwink equivalents. The impact one single twink will have on a game will be the result of their experience, not so much their gear or abilities and with that being said, will not be as strong as it was in the past. Likewise, someone whom queues up to destroy nontwinks will still have to go through extreme challenges if he wants to cap flags and win the game. Back in the day I used to be able to FC on my dodge rogue while absolutely destroying anything and everything. With stacks and the potency of nontwinks, this will not be easy. Long story short, one twink will not be able to go 50-0 and cap 3 flags whilst gy farming like we used to be able to do in the past. Twinks will die to nontwinks.
Queuing up these 4v4 WSG matches in my opinion will be more competitive than the 10v10 twink comp vs comp games we have now. In current games, the outcome can pretty much be decided upon zoning in. In these mixed BGs, it will be a challenge either way and it will require coordination to win unless you just get lucky and your team is organized and focused on destroying the other team. The avalanche affect will not be as relevant as it is today where 1st cap nearly guarantees 3-0. You may get one cap, but you cannot expect to get the next, nor the one after that.
I guarantee 99% chance that if you started twinking before WOTLK, you started twinking because you encountered a twink. Today, the only way to gain new twinks is by the previous 1% which was vocal recruitment and is less effective and efficient than pure exposure.
How many times do you guys constantly hear "No way... 19 twinks still exist?" Every week? I know on Akama, I do several times a week. People don't even know about twinking any more.