causal structure of a Turing machine simulating a human brain is very different from an actual human brain.

This statement contravenes universal computability, and is therefore false. A universal computer can instantiate any other causal structure. Remember: the causal structure at the substrate level is irrelevant due to the universality of computation. Causal structures can be embedded within other causal structures (multiple realizability).

My statement does not contravene universal computability since I'm assuming a Turing machine can simulate a human brain. Let me try another approach: Look at the space-time diagram of a Turing machine adding two numbers and compare with the space-time diagram of a neuron performing a similar summation. The causal structures in the space-time diagrams are very different. Yes, you can simulate a causal structure, but this is not the same thing as the causal structure of the underlying physical substrate performing the simulation.

It can be simulated because anything can be simulated!

Anything can be simulated imperfectly. Take the weather or C. elegans nervous system.

are there any empirical predictions where your viewpoint disagrees with functionalism?

I'm just exhibiting skepticism over claims from machine functionalism relating to Turing (and related) machine consciousness. I'm not promoting a specific viewpoint.

I predict that within a decade or two, computers with about 10^14 ops will run human mind simulations, and these sims will pass any and all objective tests for human intelligence, self-awareness, consciousness, etc.

There are no objective tests for consciousness. Of course you can re-define it in terms of self-awareness but this is not the same.

People will just accept that sims are conscious/self-aware for the exact same reasons that we reject solipsism.

Have we rejected solipsism? Certainly panpsychism is consistent with it and this appears untouched in consciousness research.