Ah yes, because everyone runs servers based on RISC-V and so -- oh wait, they don't.
I'm as big a lover of RISC-V as anyone (and am excited about the possibility of having a completely open CPU which you can load into a free FPGA). But it's delusional to think that x86 is "legacy" at this point.
x86 is dominant in the server marketplace because Intel makes the best server chips for the vast majority of server use cases. Full stop.
If somebody else comes out with a chip that's substantially better than x86 for servers, I expect the industry to transition quite quickly, just like it abandoned SPARC in the 90's.
The industry doesn't produce readily available SPARC systems, except for NEC and that European space chip consortium, plus including what's left of Sun inside Larry's dungeon, but SPARC is still evolving and is in a similar space as POWER. There are certain workloads that benefit very much from POWER and SPARC, but it's not your general purpose system that works well in a common denominator kinda way. There just aren't enough SPARC and POWER systems around to be economically viable as a x86 alternative, but technologically they're good choices for many scenarios.
The issue is that mfg of cpus at scale is very costly, and short of a large scale, the per-unit cost to cover tooling is higher... lower margins, less profit, higher cost to the customers. Per-Unit cost, and relative throughput is why Intel rules the roost for the most part, even in server.
I've looked at some of the costs of ARM servers, and they're way more expensive than they should be (compared to the cost going into phones)... I would think that may eventually become competitive... though Intel has a bit of room to lower pricing and still make money to compete.
But the chip you get in a smart phone is not what you get in a server. For one, I/O is very different and it includes things like 40Gb network silicon.
I'm as big a lover of RISC-V as anyone (and am excited about the possibility of having a completely open CPU which you can load into a free FPGA). But it's delusional to think that x86 is "legacy" at this point.