I think this is a very bad and short-sided deal.

ARM is in such a great position currently. There's no reason to sell except that SoftBank is in desperate need of capital. On top of that, Nvidia is likely to be a terrible steward of the IP. Nvidia has a terrible track record of working with other companies, partners, and open source developers. ARM has become a de-facto standard in mobile space, and Nvidia will likely use that position to strong-arm competition. This will push vendors out of ARM and into some alternative ISA. While long-term this might end up being great for RISC-V, it's going to cause a huge fracture in software stacks at the exact WORST time. Finally we're starting seeing huge convergence on ARM in Mobile/Desktop/Server space. One ISA to rule them all! Nope, now Nvidia is going to destroy that progress and set everything back another 5+ years.

Please, somebody tell me I'm wrong. I really don't want to be so pessimistic about this.

Why on earth would we want to converge on ARM? The first ARM architecture that was somewhat palatable was ARMv7, everything before that an unusable mess of different chips with vastly different capabilities. Their extensions are bad (read: subtly incompatible) late copies of what Intel and AMD are driving. Most of the innovation happens not at ARM, but their respective licensees. It took others inventing EFI to get some form of BIOS-equivalent for ARM, but even today the company gives the impression that they couldn't care less.

I agree with what you said, but there is a reason for wanting to converge on ARM.

There exists no good alternative.

ARMv8.2 or newer is a very well designed ISA, while RISC-V is a very bad ISA and I would hate to be forced to use it.

OpenPOWER is a far better ISA than RISC-V, but unfortunately most developers do not have any experience with POWER and they have the wrong belief that POWER is some antique ISA while RISC-V must be some modern fashionable ISA. Therefore even if OpenPOWER is much better, it is less likely than RISC-V to be used as a replacement for ARM.

I and probably thousands of other engineers could design a much better ISA than RISC-V in a week of work, but no one of the creators of those thousands of new ISA variants would be able to convince all the other people to choose his/her variant over the others and start the significant amount of work needed for porting all the required software tools, e.g. LLVM and gcc.

So, if ARM would no longer be an acceptable choice, I do not see any hope that its replacement would not be greatly inferior.

Thoughts on OpenPOWER vs ARM v8.2 in terms of ISA?

And for those who may be interested in OpenPOWER, https://github.com/antonblanchard/microwatt