5 years from now, it's possible that Universal will have 3 parks with maybe 8 to 10 resort hotels on-property compared to Disney with 4 parks and their 22+ hotels with many becoming partially DVC.
Also, Universal Studios Florida has been open for 26 years, IOA has been open for 17 years....that's nearly a generation of both parks being open...so people who visited those parks when they were kids will take their kids....the thing that Disney was known for and their legacy.
Universal won't overtake Disney, but the field will be leveled significantly, especially if WDW keeps losing the special feeling of years past.