Fundamental rethinks take time. The ideas expressed by the mill folks have value independent of any specific implementation or absence thereof. Yosys is incredible and the dropping cost and increasing availability of capable FPGA dev boards equally so. I wouldn't put it past a sharp CS major to whip up a toy mill cpu in FPGA these days just based on what's been shared publicly. It's a bit strange to me that I can still see echos of the Datapoint 2200 in a modern machine.
There's been a lot of recapitulation and growth in the language space recently as well, showing up in languages like Zig and Rust, paving the way for better utilization across heterogeneous and many core architectures. I feel like Rust's memory semantics don't hurt the mill either, and may help a lot.
I went looking and it seems that they're making some progress. I wasn't previously aware of their wiki, which contains ISA documentation and more: http://millcomputing.com/wiki/Main_Page
I'd also like to see further work related to this: https://core.ac.uk/reader/161119546
There's been a lot of recapitulation and growth in the language space recently as well, showing up in languages like Zig and Rust, paving the way for better utilization across heterogeneous and many core architectures. I feel like Rust's memory semantics don't hurt the mill either, and may help a lot.