I don't see you could bring something like opportunity cost into this. There's no telling whether or not they've been given a higher budget because of the massiveness of this "project".
Mixing two incompatible play styles together will divide attention, there's no way around that. No amount of money thrown at a project like that will fix that because in the end you're going to need a single director dividing his attention between both sides of the project if you want any sort of semblance of continuity.
Of course you could hire two complete teams each working on there side of the project but then it ceases to be a single project and you have to start asking yourself; why not do the much, much more sensible thing and make two different games instead without the retarded nonsensical crossover?
Terrible idea is terrible, end of story.
If Nintendo were to do a Metroid, Starfox crossover, they wouldn't just stitch together the two completely different games in a haphazard manner and call it a day. They would come up with a single gameplay approach, that makes sense for both franchises, and then they'd build a game around that. That's the sensible way of doing a crossover.
You also completely ignored my comment about good taste. But I guess that makes sense, there's no defence on your part there.
Anyway, what's all this talk about "if it's true". There is no "if", the rumour is just a fanboy wet dream, nothing more.