First of all, "enough" players aren't going to let their subs run out because of this because they're no worse off than they were before. They're still not playing the old character at all, and if they want to transfer it later and pay for it, they're welcome to do that. But you can't just let everyone who wants to transfer pick where they want to go for free right now because Fatman is where everyone will go, which will completely overtax the server. You'll have all dead servers and one server with a 2 hour queue. Is that what you want? Is that what you think is better for the game? They're much better off controlling the rush and ensuring there are multiple healthy servers. It might not make some people happy, but nothing they do will make everyone happy.
What they're doing is basically an "optional server merge," which is probably the most political thing they could do. It's no different than if there were server merges and his toons on Veela got merged with other servers that weren't Fatman. Exactly the same. But now, he'd be crying that Veela didn't get merged into the Fatman pool.
If he wants his choice of where to go, that's a paid privilege at some point in the future, after the server populations are ironed out through this method.
You're not reading carefully enough, and not getting the point.
It doesn't matter that players didn't start on a particular server on day 1. What matters is that they are there NOW. That they have legacy levels comparable to what they had on their origin servers. In some cases they have exceeded their legacy levels on their origin servers. They will not be adding any more server traffic by transferring toons to their new server.
And I don't claim to know what a large number of people will do, and neither do you. I can only suggest that it could happen, and it is a real danger that Bioware needs to address and quickly, before suspicion becomes reality.