You can still buy date-based tickets in advance. Those day-tickets will have different prices depending on assumed demand, just like it is right now.
Once you buy those tickets, you're locked in. They won't ask for more money at the tapstile.
BUT... if demand is particularly low, Disney may start selling those same dates you bought at a lower price. Which is not unlike offering a discount for those days to fill rooms and parks.
OR... demand is unusually high and the cost of those tickets go up, but it won't affect you. Your tickets are locked in. In fact, it's to your advantage that the cost goes up as demand goes up... it will discourage people from making the park over-crowded.
HOWEVER... if you wait until the last minute to buy day-tickets, you may be pleasantly surprised to see that the normal price has dropped because of soft demand. OR... you'll be steaming mad when you see the cost of those tickets sky-rocket.
This is pretty much what Broadway and airlines do. (Ironically, it was Disney that innovated dynamic prices on Broadway beginning with their own Broadway shows.)
And as mentioned above, this is for rooms and park tickets, not for meals or water.
You may be tempted, then, to get a room outside the Disney bubble. But those hotels are also using dynamic pricing. <sad trombone>
Also, resorts and day-tickets are already dynamically priced, only over a time period of a year. This new dynamic pricing will make it dynamically priced over a time period of a day or two.
