since most likely MK6 will be "online"
i'd love to see a Experience Mode put in the game.
heres how it would work:

while playing the arcade mode, climbing the ladder to beat the tournament. each fight is worth expeience (kinda like the $$ thing)

then you can use this experience points to build up levels for each character in the game.
such as:
strength
dodging
speed
defense
offense
luck

ok, example the more levels you build up for your speed chatagory (sp?) the faster you can run and attack and swing your sword.

the hole the point of this is to keep you playing to fully master all the levels for all the characters,.

but better yet, once you go online after making your character stronger when you fight other people (if they are weak) you can kick the shit out of them.

this will make going online more challenging, if everyone is equal from the start that sucks
you can make your characters more advanced .
and this will give the game more re-play value

just a thought