It's funny that I am at all conflicted on this issue given that I have been asking for the ability to faction change (in my daydreaming voice) all over the place ever since I fell in love with the horde and left behind my Alliance druid.
Yet I am.
For my Draenei shaman with her maxed jewelcrafting and mining, it would be a no-brainer. I don't care what faction she would become -- I have no special love for her mounts or racial abilities or any of her accoutrements. It would just be adding another max level character to my horde-side arsenal.
But for my druid, who was my main and progressed through vanilla and BC, raiding halfway through AQ then halfway through Black Temple, it's harder to sign up for the idea of making a switch. Yes, it would be awesome to play more often with her 76 vanity pets, and have her motorcycle for schlepping lowbie alts around on. And her collection of titles, including Hand of A'dal, isn't too shabby either.
But to make that happen, my silver haired night elf with her kitty mounts, and her purple epic flight form couldn't merely become a traitor to the Alliance. She would have to become a Tauren, which would mean a change in forms and a loss of other Alliance mounts like that braying AV ram from vanilla -- a badge of honor from my PvE guild that had a generous slice of BG and World PvP. And all those screenshots...and the LJ icons...would be of a ghost.
In addition to all of the above, there's the early adopter penalty factor. We all know anything major patched into the game is almost never working as intended straight out of the gate. Blizzard's idea of "roughly equivalent characters" may not be my idea of roughly equivalent characters. Titles and achievements could very well be lost, as could quest reward pets. As it is, despite my months of BWL farming, I don't show that I've ever completed the instance achievements-wise. Ditto MC despite having my Tier 2 pants in the bank.
So, if at the end of the day, all I would gain is having a max level druid in her Tier 7, then it wouldn't be worth it to me. I have baby alts right now I am slowly but surely leveling. I won't have max level horde-side alts next week or even next month. But that's OK. I didn't get two 80s, a 72 and a 70 Alliance-side in a short time span either. It's not a race to see how many max level toons you can drag through Naxx to soak up loot with. It's about having options for how you spend your time. And I have those now.
But I have to say, I'm excited that Blizz finally gave us the option to decide for ourselves if making the ultimate switch is worth it.