Really have no idea. They can't do anything bigger than beating Cena, Ryback and Sheamus. Facing anyone else is a step down. So I really don't know. Maybe they will end up doing Team Vince vs. Team Heyman and Shield will be part of Team Heyman.
I find it unlikely it'll be another 6 man tag. They've already competed in a lot of those recently and it would be pretty dull to simply do that again. I have a feeling they might take the tag titles at 'Mania using the freebird rule. Even though the tag titles don't mean much at the moment, it would still help Shield take another step up the ladder. Perhaps a singles match for the member not involved? We'll see.
wwe really put themselves in a corner by booking the shield against the biggest face's of the company so quick, any 3 three man combination team against the shield will be anti-climatic after already competing against the 3 biggest faces in a match.
single matches seem the only way forward for them at wrestlemania, they should though however interfere in each others matches to still show off their pack mentality that will get more heat from the crowd and make their opponents not look too bad in defeat.
reigns vs shamus
ambrose vs jericho
rollins vs orton