I'm going to disagree that MMRR will have VQ availability after 2 hours of park opening, assuming that they turn it ROTR VQ off and don't force customers to pick. The reason is, there is no trade off to making a reservation of VQ, unlike standby or Maxpass.
If MMRR offers standby, the trade off of getting in line is the loss of time you could be in line for other attractions. As the line builds, you are trading more and more time in the park for a ride of MMRR. Getting in line for MMRR prevents you from riding ToT, RnRC, RotR, SR, ect.
If HS were to switch to something like MaxPass over at Disneyland, the trade off for getting a Maxpass for MMRR is that you can't get a fastpass for another attraction until your time slot for MMRR has arrived. Getting this fastpass means no fastpass for ToT, RnRC, RotR, SR, ect.
With the VQ there is NO negative to getting one on your phone. You can get in the VQ and go get in line for another attraction AND still use your FPs as normal.
To make the system last longer, there needs to be a trade off. If there was a VQ for the teacups at magic kingdom the same way ROTR is operating, they would sell out quickly every morning, because why not get a free ride on teacups.