>> You haven't answered the point about the XXX#YYY syntax, have you?
>
> I don't understand it.

Were you referring to the examples in the SRFI?

Chicken
#<procedure (scheme#write x . rest)>
#<procedure (tween#quadratic-ease direction123 percent124)>

scheme#write and tween#quadratic-ease are valid symbols in Chicken.

 > (symbol->string 'scheme#write)
"scheme#write"

Gambit
#<procedure #2>
#<procedure #3 fold>
#<promise #6>
#<output-port #2 (stdout)>

The #<number> syntax is valid in Gambit. It refers to an object in the
same process by its "serial number", an auto-incrementing integer.

As you noticed, there is some prior art of using angle brackets
inconsistently.

Gauche
#<subr #<<parameter> 0x102ae8800>>

I'll add remarks about these to the next draft of the SRFI.