The human processing is still autoregressive, but using multiple parallel synchronized streams. There is no problem with such an approach and my best guess is that in the next year we will see many teams training models using such tricks for generating reasoning traces in parallel.

The main concern is taking a single probabilistic stream (eg a book) and comparing autoregressive modelling of it with a diffusive modelling of it.

Regarding mixing diffusion and autoregressive—I was at ICLR last week and this work is probably relevant: https://openreview.net/forum?id=tyEyYT267x