I am expecting that once Bitcoin Unlimited gets over 50% of the hashing power then they will have enough confidence to attempt to win the battle of the block size.
Possible, but unlikely. Bitcoin is permissionless. Trying to make all miners adhere to a single plan is akin to herding cats. That said...
The most widely discussed plan os to achieve >= 75% of solved blocks, hold that until the next difficulty retargeting (0-2 weeks), hold it for an entire difficulty retargeting, then start building blocks larger than 1MB (soft cap at 2MB seems to have some support).
I'm curious how this would be possible. How much collusion between mining entities would be required? Has someone done some peer reviewed research on this?