So friggin' hype for this. While any of them would be welcomed additions to the Mobile-roster, my personal ̶p̶i̶p̶e̶ ̶d̶r̶e̶a̶m̶ top picks would be:
Noah and Tiamat on the first limited rate-up banner
Sétanta as the welfare servant
Sita added to the permanent Gacha
Leave the Santas to become welfares for their own respective Christmas year (or if Lasagna wants to be evil and pull another Summer Valkyrie, make us choose 1 for this winter), and Maid-Kama for a later banner, preferably a more light-hearted event. Admittedly yes, >3 new 5 stars servants is more than excessive, but given how grandiose of an occurrence this is, I would push for the idea this would be the one time it'd be warranted. Unlikely but hey, a guy can dream right?