In addition to selling hardware, it seems like ARM-owning Nvidia would probably be happy to sell whatever amazing new ARM cores they cook up to whoever is willing to pay to use the design. It's not obvious RISC-V will benefit from any of this. Somebody, somewhere would need to create equally amazing RISC-V cores and find a way to sell them.
First get C, C++, Go, Rust, Java, Erlang, .NET,.... generating competitive native code, port all their main libraries and IDE tooling, and then it might stand a chance.
You're right that a number of mainstream software packages are still work in progress, for example V8 doesn't target it yet.
But RISC-V is thriving in other areas like industrial controllers, and Alibaba Cloud just announced a few days ago they are using it in a new server processor, positioned as an eventual competitor to AWS Graviton.
Topically: Nvidia uses RISC-V in some GPUs as a controller (not the GPU core). Not sure if those are released yet, but they gave a presentation on it at a recent RISC-V meet-up.
My impression is that the Cortex-Ms are popular because of the price, the rich sets of peripherals they tend to come with, and not least because they come with a proven, performant C compiler. I don't think it's impossible that a RISC-V core could make some dents in this markey fairly quickly, especially if Nvidia make the future of the platform look uncertain.
I'm still not sure, after reading all these comments, why anyone thinks an Nvidia that owned ARM would do anything other than continue to sell ARM cores and ARM IP rights to other companies, as well as continuing to sell actual hardware products using ARM cores. Suspecting the worst in everything is sort of standard nowadays, but buying ARM Ltd. so Nvidia can stop promoting the platform and selling the IP does not make much sense.
(unless they literally have a master plan to drive everyone back to AMD64, which doesn't make any business sense since they can't make that hardware, or drive everyone to RISC-V and profit off of that, which doesn't make any business sense since they could attempt that without buying ARM Ltd. and spending tens of billions of dollars)