Capcom’s recently released (Apr 18th) forecast for the future shows that they plan to put DLC at the forefront of their business strategy with an attempt to make more profit off of digital content.
Considering the timing (obviously this whole forecast was put together over the course of several weeks with discussions before hand.) it seems logical that the somewhat surprising turn of events of having an SF4 update would coincide with this new direction for Capcom. Also keep in mind Capcom has specifically stated that they are being vague about the platforms the stuff is releasing on (Points to the idea that they may be releasing another “AE” style disc version and porting the game to either Vita, WiiU, or PS4). Then you have the suggestions forums for changes, and while perhaps I’m reading too much into it, it is worth noting that Combofiend said quote “the skies the limit” in terms of system change suggestions.
Then you have the interest shown from trollNo about the modded version of Rolento. You have the large number of requests to bring the 4 characters from SFxT over to SF4 (Rolento, Elena, Poison, Hugo) and fixing the unblockables may require a modification to the engine itself (Similar to Vanilla to Super or SF4 to SFxT.)
Ono also stated previously that he would want to add more features to SF4 if he ever got the chance to do an update. Now this is of course him saying something he’d WANT to do, that doesn’t mean that it is something he got permission to do.
All together there is a fair amount of circumstantial evidence and plausibility to the idea that this may be a more in depth update along the lines of AE or even Super rather than something like AE2012 or even SFxT 2013.