> Of course, there's nothing to prevent you from renaming standard lambda out of the way and using keyword-lambda as lambda, at least in principle, though using import to mess with the names of fundamental syntax forms is going to be problematic.

Guile's module system has "#:replace"
(https://www.gnu.org/software/guile/manual/html_node/Creating-Guile-Modules.html#Creating-Guile-Modules),
which allows imported bindings to override already imported bindings
by the same name. Some edition of R7RS-large may allow an export spec
of the form (replace <identifier>).

> And plain application has no syntax keyword, except in Racket where it's #%app (ugh).

Why "ugh"? I'm not talking about the name. But if it were possible to
parameterize plain applications in R7RS-large, a lot of great syntaxes
could become derived syntax, including a SRFI 177-style syntax without
a keyword like "keyword-call".