I think if they made a movie it would end up containing the following elements:

a.) Some sort of a big adventure with the mane six (and possibly Spike) traveling across Equestria
b.) Some sort of big scary villain (Discord/Nightmare Moon but on steroids)
c.) There would probably be a split up at some point, leaving Twilight alone
d.) The theme of friendship would be really hammered in for a big flashy finish with all of the ponies
e.) Cutie Mark Crusader subplot, they may or may not get their cutie marks
f.) Tons of great musical numbers

This is how my Moviemaking Sense tingles, anyway!