Both Amirouche and Marc expressed in the other thread that keyword
lambda syntax is "heavy". Since both of you feel that way, there must be
an important issue there that we should explore.

I don't quite understand the heaviness on the define/kw side; to me
define/kw code feels lighter than an ordinary `define` followed by a
separate let-keywords or let-optionals.

Are you talking about call/kw? I agree that requiring a special prefix
for procedure calls is heavier and ideally could be avoided. (But as
John explained, it can't be avoided in R7RS-large unless the charter is
changed.)