SRFI 169 is due to be finalized tomorrow (25th).

The current spec is fairly conservative. If anyone is still interested
in adding underscore support to their Scheme reader but finds something
objectionable about the way it's specified in the SRFI, please voice
your opposition now :)

I can still:

* restrict the scope a little if there is some particularly problematic
interaction with another language feature

* clarify the explanation

* add more examples