Ask the existing R6+R7 implementers?

[Lassi Kortela]

Another way to get started working out the details R6+R7 compat
(including syntax-case and library compatibility) would be trying to
gather the existing implementers who already support both standards in
one place:

- Kawa
- Guile
- Loko
- Sagittarius
- Digamma (successor of Ypsilon, runs on LLVM)

We might also be able to convince the following R6-only implementers:

- IronScheme
- Mosh

This might be easier than going directly to the major R6-only or R7-only
holdouts like Chez, Chicken, Gambit, and MIT.

(It's virtually certain that no force on earth will move everyone to
adopt syntax-case, so any joint standard should have it as an option. I
remain hopeful that R7 implementations would add support for the R6
library syntax.)

[Lassi Kortela]

And of course Larceny, if we can convince its maintainers to revive
interest.

I just sent a very brief email to Andy Keep from Chez asking him what
it'd take for them to implement a new RnRS. He does not always have time
to respond, but sometimes he does so it's worth a try.