Thanks to a tip from @alex_mmorales it looks like we can expect the Playstation Vita version of Mortal Kombat 9 pretty soon actually. Within about just two months away on April 27th, 2012 according to the UK Playstation site, we'll be able to play some MK9 on the go!
Source: http://uk.playstation.com/psn/games/detail/item450889/Mortal-Kombat/