We would like to send expressions up to the Dask scheduler have them optimized and lowered there and then enter the normal scheduler state. To do this I think that we need a new route on client/scheduler communication. Maybe that can be made more general and accept "something picklable that satisfies the .__dask_foo__ protocols" or something similar.

Eventually I'd love it if we held on to the Expr structure in the scheduler to inform future optimizations, but as a first pass I think that we probably just try to end up with the same state that the current update_graph route achieves.

@fjetter I think that this would benefit from someone on your team