I just can't see that - they aren't going to invest even more to pimp the competition's product.
I honestly don't think that Universal is all that heck bent on keeping Marvel. They've been content with it for awhile, but eventually - I think that's a very large plot of land that could be very easily re-purposed for something else they have the rights to that isn't nearly as complicated.
I mean, when you think about it - they could re-theme MSHI practically overnight. Besides Spidey itself, the other attractions and features are all flat facades and signage that makes it "Marvel", which are easily replaceable. Close up Spidey and re-theme it, and they are all set.
Ten years ago, getting rid of MSHI would have been unthinkable - it would have been like losing a major organ. At this point, post-Potter (and Simpsons, and Transformers, etc.) it's more like a gall bladder. It doesn't hurt to have, but it really isn't a great loss to lose.
Given how forward thinking, and moving, Universal has been - I have no doubt that plans have already been drawn up for that eventuality, when they have something else they want to put there.