That might be a marketing move. It seems like they’re trying to keep I-Rap a little hidden. The newest trailer removed quite a bit of the suspense behind it though.
One would assume that hybrids would be discussed, especially if people saw JW (Which, there were a LOT).
And that, perhaps it's just me, but I am seeing a lot more marketing for the I-Rap than I did of the I-Rex.
But in any case, I would also assume that if the JW conversion happens for River Adventure, it will not radically change the plot to include the I-Rap instead of the I-Rex.