I agree (and hope) that RISC-V will become very, very significant.

That doesn't mean that ARM 'is going to die'. RISC-V is not 'free' in the sense that someone has to design an implementation that works for you - and then support it. The economics work for WD but not necessarily for everyone - not everyone has WD's scale. Plus price isn't the only factor in choosing an ISA / implementation.

It's entirely possible that due to the modularity of Risc-V some kind of common ground will be found in terms of common extensions( a de facto standard, i.e. a standard that people actually follow). Then you might have companies licensing designs for bits of the SoC so the total cost of developing a full SoC drops. This is happening to an extend already seeing as you can buy gpu or hardware accelerator tech from various companies.

I'm not sure what the gain is here. We have to hope that a standard emerges from a range of extensions - when there are standard ISA's that do the job already. In the meantime we get lots of incompatibilities. Plus there is the possibility of proprietary extensions which are not available for licensing more widely.

Licensing IP to put on SoCs has been common for over 25 years - in fact its the whole basis of ARM's and others business models.