I'm a donator on Nethalion- I've donated a lot. I love solo queue arena (and 1v1 arena). If they add it to Nethalion it will make me very happy and I will likely be motivated to donate a lot more. I've talked to some of my friends on Nethalion who agree.
On the other hand, if they give that feature I really want to some AT guys in basically free Cata gear on Warsong, who probably never donated to and don't even like Molten, it will be a sign that they are looking to favor the AT guys on Warsong, more than they already are (which is a lot).
I don't want to transfer to Warsong, by the way. I like being on a server with a real economy, and I like being able to defend my undergeared herbing druid with my geared hunter, when someone ganks my druid.