From MPQ Twitter and facebook:
Watch the Marvel Games Panel (Sat.) at #SDCC and check out our new trailer and updates coming to #MarvelPuzzleQuest marvel.com/sdcc2014.
So what are they holding back for the Saturday announcement?
No news over at marvel.com since Feb 2014.
The hero points sweepstakes is on until Jul 27.
That they are adding in more characters
changing all the characters powersets
changing the pricing structure for leveling
adding / removing the amount of covers for a maxed character
adding / removing colors from all the characters
changing the cover art to crayon drawings done by one of the interns 6 year old
giving everyone a free bagman (oh wait they do this already)
adding varents of all the exsisting characters in all star ranges (hello 1* Nick Fury)
Demiurge_Will mentioned that there is something hush-hush in the pipe that he is excited about.
I doubt that it is simply new characters since that doesn’t seem worth mentioning, but I don’t want get my hopes up. I would love it if they finally found the time to add some fun, non-competitive content to the game. But there I go, getting my hopes up.
Something else I’ve heard of – MPQ digital code souvenirs at SDCC. I have no idea what these would be.
It’s probably the retail version of the game that got leaked a couple days ago, if rumors can be believed.
Hmm; hard to guess really - imagination rather exceeds the scope of changes that have actually happened in 2014. 
Realistically, I would guess…
Achievements (re)announced.
Titles, tied to achievements & other things (e.g. the ‘digital souvenir’ Nonce Equitaur mentions above).
New character silhouettes - not Guardians of the Galaxy, but maybe X-Men & Dark X-Men.
Extra bonus wild guess - one silhouette will be Wolverine, again, ultimately revealed as a 2** ‘Logan’ version of Patch to great annoyance of forum-goers. 
N.B. I am intrigued by this “retail version” talk - what would that entail?
Honestly I am guessing:
Raids
Improved 4* class
Something else totally unexpected on level of “alliances” or “seasons” (for good or bad they have changed the game)
A retail version does sound interesting. MPQ has a ton of content (mainly characters) that I bet most new players will never unlock. If I were a new player I would feel pretty left out and question why I should buy 12 roster slots for 3* characters that won’t be playable for at least 6 months. A retail version could change that.
I guess it’s a question of what it should be and what it will be. For example.
Should - Wonder if they are going to rebrand to just MPQ and drop the Dark Reign tag - theoretically gives them a lot more leeway with everything.
Should - I would love to hear about a complete character overhaul (like the stuff I have suggested in my reclassification threads) but not holding out hope.
Should - A more streamlined way that all sorts of random amounts of ISO and covers are given out.
Will - Regardless of anything, I actually think it’s going to be something quite new like new gameplay styles or maybe building of a base / HQ or even a total overhaul of the cover system and how they are gained. I think it will be one or more things that have may or may not have been mentioned in various threads, but none of us will really be expecting (starting off with reasonably low expectations, sadly). And it will be quite interesting / cool and likely to positively surprise.
The other way of looking at it, is that it’s essentially going to be MPQ v.2 with several significant changes and/or additions. Perhaps why they have been so quiet here in the recent weeks / months.
5* characters?
Or a new mode/format.
there are only 3 4* characters. i would be pissed if they came out with a 5*
A 5* would make me immediately uninstall the game. Been playing since launch and my 4* heroes are nowhere near a usable level even though 2 of them are essentially cover maxed. Don’t need a two year grind for one character haha.
I’m hoping for some new modes of play, and hopefully some less stressful ones at that.
I know that one of the other games on that panel is announcing some Axis event tie-ins. Maybe…I dunno.
I’m hoping for:
I am expecting:
Maybe they’ll announce that someone has given them a world map and ZOMG, there’s a whole other continent (or two) on the other side of the Atlantic!
Would love to see:
Cover Trading.
A Spar feature that allows you to practice against your alliance.
Please no cover trading. The game has enough exploits as it is.
My guess is the ‘big announcement’ is going to be that the game will be released on PSN/Xbox Live.
What for? It’s not like you will be able to carry your account over to it…
It’s not for you silly, it’s for them to get more players and more possible revenues.