Yes, that's where AT&T is more logical.

In practice, though, naming a symbol with a register name is error-prone and confusing. I'd rather have a way to escape a symbol when it's really needed than to pay the price of noise for an admittedly bad idea.

New registers are added all the time (for instance, the %zmm registers), so even if a symbol name doesn't conflict now, it might conflict in the future. Having separate namespaces for symbols and registers is a good idea.

Good point, but I wonder if it shouldn't be the labels which should be prefixed instead of the registers?

Yes, ideally the labels would be strings in the style of C source code. That includes using \0 to put NUL bytes in the middle. It also includes wide character strings.

This allows for unusual languages like LISP and FORTH, without mangling the symbols. Symbols could have commas and spaces.