Never saw this coming.
I don't think Disney will start restricting Uber rides until congestion becomes an issue. Ride-sharing makes traffic worse, not better. The new Lyft agreement will probably just be marketing. Uber doesn't need the advertising as much because they're a much stronger brand name.
The Minnie Van part is where this gets interesting. I firmly believe that people get Minnie Vans because they don't trust ride-sharing. In 2019, there's a large segment of the population (more suburban, more car-oriented) that doesn't trust Lyft/Uber drivers because they're "unverified" strangers who might be serial-killers. Those people would trust Disney's Minnie Vans because those are driven by Disney cast members and therefore inherently trustworthy. Ride-sharing rider demographics don't completely overlap with Disney World visitor demographics.
But now, if Minnie Vans are being driven by regular Lyft drivers (i.e. strangers), the whole value proposition for Minnie Vans gets thrown out. Minnie Vans do get special pick-up/drop-off locations though. It makes me think Disney will lean more into priority access as the defining feature of Minnie Vans.