I don't want to write nt(a=1, b=2). That's ugly. I want to write (a=1, b=2).

Being able to implement it without changing the syntax is irrelevant to the users of the language, mostly. It's an implementation concern. I've always felt that being a little harder to implement isn't a point against a feature, if it's good for users, because even a small improvement for users is usually much less effort in total than even a large implementation effort.