I'm not a specialist in CPU design but to me RISC-V seems like an incremental evolution, nothing really ground-breaking, when compared to alternatives the main benefit is the openness/licensing/cost. But at the same time think that you can get a $5 raspberry pi and embedded ARM chips cost pennies.

The entire effort of supporting it and building the ecosystem will be hard to justify economically at these cost figures.

Mill on the other hand has a lot of interesting ground-breaking ideas that can potentially offer a 10x performance/watt improvement.

Many people have been recently in awe after experiencing the ARM performance improvements around 40% offered by the Apple silicon and AWS Graviton CPUs. Just imagine something offering a 10x based on a Mill design, I'd love to see it built one day and available on the market.