As far as I can tell this isn't any different conceptually from the distributed inference setup that PyTorch/Huggingface Accelerate/etc support. Of course those were built for cooperating machines owned by the same organization with lots of high-speed I/O. In an @home/BOINC setup, you need to package things up into work units that get sent out to other people's computers, and you don't get anything back until the end. So it's higher-latency and you have to worry about people cheating the system with bogus work.
I'm not sure if this would be more efficient or cheaper than just renting out a bunch of AWS spot instances with GPUs in them.
The main problem I believe is that you would need extremely high bandwidth. For a 100B model you're looking at 400GB of gradients you need to send each batch. There's a reason why super fast networking is used.
[1]: https://www.together.xyz/blog/releasing-v1-of-gpt-jt-powered...
No copyright on an AI if it was machine generated, which the training is. Great catch kmeisthax!