Well, assuming this turns out to be true...I want to speculate.
Who do we know would WWE want to set up a feud with, or go nostalgic with.
Let's weigh our options:
On the nostalgia side, we have an easy and very likely candidate=Vince McMahon. What better way to celebrate Raw than with the ultimate feud between two of the greatest and arguably most household names from this business. It's a great blast-from-the-past-type moment and it would get a huge O.
We could also see the nostalgia in having Austin stun The Rock and set-up their final Wrestlemania encounter that the fans have wanted since they both retired. Especially considering the big "Austin Rocky" chants at the HoF ceremony.
For story building (and in the second instance I expand on, nostalgia additionally), there are two MASSIVE candidates.
Austin could come in while Brock Lesnar is bitching, and stun the hell out of him (and everyone else). This would seem unlikely, as Triple H is all but certain to be facing Lesnar at Summerslam. They could open up a special ref spot for Austin in that match, and then potentially set up an Austin/Lesnar 'Mania match. That seems too big for WWE creative's britches though.
My second idea is that the Undertaker would finally return to the ring, only to be challenged by the Texas Rattlesnake for the upcoming 'Mania. This would be HUGE because THIS WOULD BE an end of an era match. There aren't many people left for Austin to face, other than newer talent, so why not let Taker go out in a blaze of glory, battling it out with Austin where either Austin wins, or they both just can't continue, or both win/lose.
Now I only think it will be an outsider to the main roster because it seems like WWE is pretty occupied with everyone else on the current WWE roster.
My personal favorite would have to be Austin/Rocky III (or is it IV by now?), but i do like the potential for an Austin/Take feud leading up to Mania potentially.
What does everyone think?
The only current guy I could see feuding with Austin would be CM Punk, as they have been somewhat tight via twitter and just relative conversation (and comparison).
No chance in hell: Austin will not stun Triple H. This is especially because of the DX reunion.