As has already been mentioned a number of times, Yoshi already said he thinks SAM should be DPS. Given that, I really think the chances for SAM as tank are pretty low.

Something hammer based would be cool. And another tank that shares the shield with PLD would be interesting. I could see Templar as a good option (1H Lance + Shield).

Maybe even BLU as a tank. As the BLU is all about getting hit by monster abilities to learn them, it makes the most sense to me if it were a tank here. Granted, it wouldn't be the same where you permanently learn 40 or 50 skills and choose between them. Instead, a BLU here could absorb specific skills to get limited use charges to use within the next 30s or so. For instance, if hit by titan's table flip, it would give them one charge of that ability, and they could turn around and use it right back (a scaled down version, obviously).