Yes. Setting up the sentinel network is definitely the difficult part of deploying a sidechain under this proposal.

The problem with unfederated sidechains is how to allow withdrawals without requiring Bitcoin nodes to run sidechain nodes.

Drivechains, on one end, make withdrawals really slow, giving miners time to receive feedback and nodes to respond indirectly. Softchains, on the other end, use fraud proofs and require sidechain nodes operate on rules similar enough to Bitcoin to allow Bitcoin nodes to validate contested sidechain blocks.

Sentinel chains are designed as a middle ground, where nodes can hold miners accountable directly and automatically, but still don’t need to run sidechain nodes. But the trade off is that they must rely on a network of distributed trust. Making sure the sidechain has broad community support with the desire to hold miners accountable is critical to a particular chain’s success.