As was mentioned earlier, Freddy and Jason were leaked to be in MK9 at some point, but the "rumor" was deterred only to now be proven true, halfway at last. Now think of this, Freddy vs. Jason 2 has been in development for years now, slated to release in 2006, 07, 08, and 2010. Is the inclusion of Freddy and potentially Jason down the road an indication to this? Hopefully. I'm sure we can expect something around Halloween from NRS concerning Jason. This is probably Warner Bros. way to gauge interest and an iconic horror franchise and see if a reboot is worth their time.
Concerning Freddy vs. Jason 2, Micheal Myers was rumored to join the cast as well. More future dlc? Fuck it, bring it on. More overpowered guest characters. *In half hearted reply* Yeeeeeeaaaahhhhhhh..... :\