Ever since paid transfers were introduced, quite some time ago, there has been one very prominent restriction: no transfers from PvE servers to PvP servers. The general reason given for this is that it wouldn't be fair; people who level to 70 on a PvP server have a significantly harder time of it that people who do it on a PvE server, and letting people transfer from PvE to PvP is just going to encourage them to level where it's safe easy and then transfer to go around ganking and raiding and whatever else they want to do. Well, that restriction is lifted: paid transfers from PvE to PvP servers will be available
from now on.
Blizzard's stated reason for this is that "providing a smooth and enjoyable experience for all players is always a priority for us," and that these transfers are being implemented "to provide players with more mobility and freedom to easily play with their friends." While these are valid reasons to a certain extent, I still think this will be pretty unpopular with players on PvP servers.