That about sums it up.
There's no impact on anyone else if someone wants to switch their AC.
There's a possible minor impact on EA/Bioware's bottom line. Anyone who desperately wants to switch a Shadow to a Sage may potentially not play as long as they would if they had to re-level, but EA/Bioware have shown little concern at all about allowing people to speed their way through the game for cash.
It will also affect BW's bottom line with the loss of subscribers if they allow class changes. You can try to fool yourself all you want, but allowing class changes WILL cost them subs. As I said, only BW can make the determination if the possibility of revenue from those who might pay again if they allow class changes is worth the risk of losing those ARE paying now and would no longer be doing so if they allow class changes.