Re: But landfilling means zero RoI for the product.
They may be useful for non-crypto compute, but as far as I can tell no one has embraced GPU for production compute
CPU-GPU architectures are pretty common for high-performance scientific computing, and for running convolutional neural networks as part of "deep learning" systems. There are certainly non-crypto production applications.
Granted, there aren't a lot of CPU-GPU applications for general business use, which as you say is typically I/O-bound. But even for traditional business there are potential applications such as Dynamic Stochastic Vehicle Routing, which is of interest to many firms that deal in logistics.