Decentralized applications could submit their transactions to many of the 64 available clusters, which compete together for fees and slot availability, and have internally a node distribution algorithm. Building a collision in such a disparate and competitive business framework is at least as hard as preventing the current Proof of Work mining pool concentration.
In addition, once the fraud detected, remaining honest clusters have a high incentive not to collude since they get slot stacked tokens from faulty clusters. The stronger the wrongdoing colluding group, the bigger the reward for honest nodes. Knowing this, applications should take small clusters in their validation requests that are not aligned in interest to join any group of strong wrong doers.