EDIT: From Blizz's own blog post on WOW TBC Classic Gold the topic. "On Patch day, players will be able to launch the Battle.net desktop app and select which game you'd like to play, whether it's Burning Crusade Classic and WoW Classic. Both types of games will display your existing characters under the old realm name/s. After choosing a game, choose a character that you would like to play and then confirm. If you decide to play your character in both game types You'll be able to use an optional paid service to gain access to the cloned version of your character in both game types. All you need to do is log into the game as usual and begin playing.

Because the copy is complete prior to release and is released. All the characters exist in Classic which means there's no copy-downtime if you select Classic. TBC may cause downtime just because it is not instantaneous. It may also lead to more characters being copied simultaneously. This could result in the system being unable to function properly.

Bots are most likely to benefit from the boost, which makes it more difficult for bots. However, if bots were properly managed, I don't think it would be as any issue. My family and I come back to classic as we enjoy the tbc. They only join because they have the ability to increase their levelling content.

Every character we have is in Classic already. They don't want inactive while others go to TBC. All characters will be cheap Burning Crusade Classic Gold copied before launch. If you choose TBC then they'll flip the "active" aspect of the TBC database to true as well as flipping the "active" bit on Classic database to false. After that, you'll pay them $35 to flip the Classic bit back.