Nice thought, I thought about it too.
I think pollinating flowers in the wild is a gamble. Fruits taste the same and initially have no advantage.
It would be easier to plant a hybrid aside. More fruit, more chance of distribution by animals, perhaps cross-pollination, but it still takes generations.
Malus sieversii is said to have been developed by bears through natural selection. If so, then it still took thousands of years.
There might be already hybrids in nature. I've never been to the USA and I can't judge it. But I got seedlings from the wild when it was still legal. It turned out that they were hybrids.
Just a thought game:
I wonder whether the typical Poncirus taste could be advantageous in nature? If animals prefer citrus fruits, as you observe, there should be seedlings around citrus plantations (especially some time ago when seedless varieties were not so common). Not necessarily much, but there should be. If there are none, the seeds seem to have some disadvantage. Maybe animals eat the seeds with them.