I doubt it will be about any character or story that has already been written, but rather something entirely new that fits the action in the new movies, rather than the existing extended universe.
Of the things listed a re-appearance of Boba Fet seems most unlikely. As far as the movies were concerned, Boba Fet fell into the Sarlacc and that's it. That he survived it and cut himself free out of the belly of the dragon is an EU thing, but I don't think that they really have to succumb to recycling already defeated villains to make up a good story - doing so is actually a pretty cheap trick of the trade.
The most likely thing is that a newly introduced character that only appears briefly in Star Wars 7. Like in the matrix video games that take place between Matrix 2 and 3, Ghost and Niobe were the protaginists.
As to what I wish for - that is hard to say. Not another adventure movie maybe. Something that toys with the concept of the Force and its implication, but maybe is rather a detective movie. Or a drama of a falling knight. Maybe something that is not so heavy with action.
Or it may be the story of a war ship or so (recently seen "Das Boot" and "The Caine Mutiny" again - I like those). Action, but darker and limited to a very confined space....
However, it should have a smaller scope, not this gigantic, galactic spanning plot, but, compared to the actual Star Movies present a "small picture".
Boba Fett is a tremendous hinge character. I mean, without him, Jaina doesn't learn how to fight so Darth Caedus (her brother Jacen) can counter her, which likely means she loses. He has a tremendous impact on the Yuuzhan Vong by leading Mandalore during the invasion. If what you want happens, then the entire EU would likely need to be ejected. Boba Fett, being dead, doesn't challenge Han Solo and allow him to live, so Solo doesn't straighten up and court Leia, the Solo children are not born, end of EU. It really is as simple as that.
Whatever the new movies are, you can bet your bottom dollar they won't stray from established characters. Myself, I would be okay with Hier to the Empire, even though that is extremely unlikely. I would dearly love a focus on Rogue Squandron, particularly the Bacta Wars and Isard, with leading roles for Wedge Antilles and Tycho Clechu, but there won't be enough Force **** for mainstream audiences.