[gpderetta]

what would it break? It litterally was proposed by an extension, with support from Stroustrup.

IIRC Stroustrup regrets using . for member function calls (as opposed to just some syntactic sugar for any function call)

[leni536]

The way it was worded in the GP comment would change name lookup in existing well-formed programs, making them fail to compile, or compile differently.

I'm not familiar with Stroustrup's proposal, but I doubt that he proposed it without some opt-in annotation.