[Jmacq1]

Ultimately, if the crossover is purely at a "toy" level and not an actual blending of mythos it can probably work. Arguably there are two different types of crossover to be discussed here: The type that's purely conceptual (as we see with the Star Wars and Marvel Transformers lines, or the various Mr. Potato Head variants we've seen over the past several years), and those that blend the actual storylines and characters together (Like the G.I. Joe vs. Transformers comic book series). The first version obviously can work on some level, but the latter is almost impossible to maintain in the long-term, whether due to licensing conflicts, dilution of the fanbase (some of the hardcore fans of either franchise will no doubt dislike the crossover idea/feel that it's "stealing thunder" from their favored half of the franchise), and likely a lack of media support (because licensing out a Transformers/G.I. Joe weekly cartoon would be twice as hard as licensing out one or the other). With the mass-media tie-ins, it's very difficult to maintain long-term popularity.

I do think there's some room for crossover, but largely with defunct properties wholly owned by the same company. For instance, I could potentially see MASK and COPS as sublines of Transformers (Think Human Alliance-style toys for MASK) or G.I. Joe.