My hope is that it's six men involved in the match (three teams, one man to a pod). Having 12 men and six teams would be a bit of a fuster cluck. It would be hard to follow watching from home, although logistically it could work with men tagging in and out, but why would you inject order into chaos?
I'd pit New Day against Cesaro/Kidd and the Lucha Dragons. I'm a bit torn between Luchas and PTP, but since PTP haven't been wrestling, I'm going with the Dragons. The luchadors will make for an exciting match for high flying spots within the chamber. Imagine Kalisto spinning off of a pod. I've been wanting to see Cesaro and him back in a match for a while now. PTP will re-enter the title scene soon, but knowing WWE they might wind up in this match.
If they decide to do 12 men, take the three aforementioned teams, add PTP, the Mega Posers (see what I did there?), and the Ascension. I think the 12 man might be too much, if they went that way though it would essentially be tornado tag team rules, with all men being valid in the ring at once. There would have to be an early elimination, so look for Ascension to start against the Luchas and not make it to the first pod opening.
I'd prefer a three team match, and it would be much better for presentation to the home crowd. A 12 man match would be a chamber first (for what that's worth) but it might be difficult to follow. A new IC champ doesn't necessarily mean that the champs retain (there have been shows where all titles have changed hands, there will be again). My prediction is Kidd and Cesaro capture the titles here for their second reign.
Edit: ps, totally forgot about the reunited former Wyatts. Scrap Ascension in my prediction and sub Harper and Rowan in the six team scenario. They will be contenders for the third spot in the three team after New Day and K/C.