Using such a VM requires rewriting existing C code. Wasm's approach allows that to happen incrementally, where it matters, by using memory safe languages like Rust, instead of relying on the VM.

Not at all, as proven by memory tagging on Solaris/SPARC, iOS and upcoming Android/ARM v8.3.

So leaving memory tagging out of WASM was a deliberate design decision.

There are already better alternatives to write secure code if using C is not a requirement, so again nothing new on WASM other than its hype.

Sure, and we use software memory tagging with things like LLVM sanitizers. It's great.

But a) the hardware Wasm needs to support doesn't have tagging, and b) the software equivalent requires support from the allocator and has a large performance penalty.

So yes, it was a deliberate design decision, taken in order to support existing C programs on the Web.

This is really getting tiring- learning from the past is great, but fetishizing it to the point of denying anything new has any value is... not.

WASM wouldn't even be a thing if it wasn't for Mozilla politics against PNaCL.

Tiring is the continuous advertising that WASM is the second coming of Christ in VM implementations.

Those "politics" were there for a reason. Wasm is a solid improvement over PNaCl, which I will note you have curiously left out of all your other old-VM-worship claims.