MS also agree that the primitive __m128 is the right approach. I'm not basing my

opinion on their judgement at all, I independently conclude it is the right
approach, but it's encouraging that they agree... and perhaps they're a more
respectable authority than me and my opinion :)

Can you show me a typical example of how it looks in action in source code?

What I proposed in the OP is the simplest, most non-destructive initial
implementation in the language. I think there is the lest opportunity for making
a mistake/wrong decision in my initial proposal, and it can be extended with
what you're suggesting in time after we have the opportunity to prove that it's
correct. We can test and prove the rest with libraries before committing to
implement it in the language...

I don't think the typeless approach will wind up being any easier, and it'll certainly suck when it comes to optimization, error messages, symbolic debugger support, etc.