I don't think you need to be worried about more than 2-3 players in all of the B1G transferring to another school and playing right away. They would need to be grad transfers and top-top players. That's not the issue.
The issue is that the B1G is pushing for a spring season. That season will be played during the NFL draft, and abbreviated which will hurt anyone who wasn't already a round 1-3 draft pick (all of those players will have already opted out).
Moreover, I think the B1G is going to look at the scholarship situation and realize that they will need to toll these players if they want to keep budgets under control. That means possibly no opt-out on the spring season or an automatic toll anyway. That's what they did with spring athletes this year. If you were a senior, then you were just done, too bad for you.
If you're a player like Durr in that situation, then it would be in your best interest to transfer and sit out for a season rather than play only 2-3 games in the spring before the draft.
A spring season will require a ton of work and the fact that they just floated the idea instead of laying out an actual timeline tells me that they haven't even begun sorting through all of the implications of what they're suggesting.