I would not be surprised if the Joker was in Batman Vs. Superman. The trailer hints that the Joker will make an appearance. The Joker appears in The Dark Knight Returns, and BvS seems to be ripping it off wholesale in terms of action and plot. There are items which suggest his appearance. The newspaper:
And the "Ha Ha Joke's on you Batman" scrawled over Robin's costume:
In DKR the original Robin Dick Grayson is dead, and his costume in the BvS trailer seems to suggest that Robin is also dead in this movie. The way Bruce Wayne looks at the empty cowl further suggests that he is retired or semi-retired at the start of the film and brought out of retirement to deal with the issues raised by Superman's debut.
Then there's the rifle scene:
This shot of Batman holding a rifle is an obvious callback to the part in DKR where Batman curiously dawns a rifle:
I submit that, therefore, this movie will be entirely unoriginal, a direct rehash of the Dark Knight Returns. If anyone wants to know the plot or the ending of BvS, one can do so by picking up a copy of the comic book or watching the adapted Dark Knight Returns animated movie.