That's a good idea. A bigger problem than time-slicing is probably GPU/TPU device ownership issues and GPU/TPU memory usage with multiple games going in parallel. There may be some ways to multiplex it intelligently though.

Costs are difficult to work out - it depends on cloud vs. self-hosting, what kind of TPUs/GPUs, how long you're calculating over.

The advantage that classical/NNUE engines have is that they can more easily spread over distributed frameworks like Fishtest.