Can the structured bindings syntax be used in polymorphic lambdas

This is not currently allowed by the syntax; structured bindings are a simple-declaration:

simple-declaration:[…]
– attribute-specifier-seq_opt decl-specifier-seq ref-qualifier_opt [ identifier-list ] initializer ;

while function parameters are introduced by a parameter-declaration-list, which contains declarators:

The declarators specify the names of these entities and (optionally) modify the type of the specifiers with operators such as * (pointer to) and () (function returning).

That is, a structured binding is a (block-level) statement syntax – you can see this by noting that the grammar for it ends in a semicolon ;. Allowing structured bindings in a lambda parameter list would require additional grammar to be added.

It sounds like a good idea, and I can’t immediately see any ambiguity in the syntax; it would certainly be worth discussing as it solves your presented use case nicely and more concisely than the alternatives.