I like the idea of getting acknowledgment for earning the Christmas skins, but I don't think it's fair for newer players to be locked out of 22 unique skins just because they weren't invited to the game's alpha. Also, I'm pretty sure most of the cast are just going to get new models in general, so the current Christmas models won't hold up for long.
I'd be fine if we did keep them, but I wouldn't make them one-time only or tradable.