Mash-Ups of different franchises are often a bad idea. In most cases they end up not pleasing fans of the two separate properties and the end product comes out as something that is considered a failure by everyone involved. Horror fans need look no further than FREDDY VS JASON or ALIEN VS PREDATOR to see a couple of crowd dis-pleasing cinema mash-ups that were far less than the sum of their parts.
Of course, what doesn't necessarily work onscreen can sometimes be made to work on the page such as the excellent Alien vs. Predator Dark Horse comics from the 1990's that could have been the template for a better (if not great) film. Also, there have been some fascinating Friday the 13th comic book series that have incorporated elements from outside the film series to good effect including crossovers with Ash from the EVIL DEAD films. And there are a host of non-graphic novels out there that extend and add to various cinema series in creative and entertaining ways that please the hardcore fans who are the obvious target audience for these 'extended universe' stories. Hell- I'm still trying to collect the entire run of Friday the 13th novels written as sequels to my beloved JASON X!
So, it appears to me that the best way - for now - to continue to create successful mash-ups is to do it on the page and for a case to make this point I give you IDW and Boom Studios new comic book series Star Trek/Planet of the Apes. At first glance I was harrumphing at the very idea of slapping these two very different types of science fiction together. They clearly exist in extremely different universes both in subject matter and style. There seemed no way to place the original Star Trek crew in contact with the Planet of the Apes post apocalyptic world that could possible make sense. The very basis of classic Trek is an optimistic view of the future where many of the problems we think of as insurmountable have been solved. But the basic premise of POTA is that mankind was so short sighted that they couldn't keep from destroying the world. How to put these two franchises together in a way that did not compromise either one?