Talking about writing something without actually thinking it through enough to write it, that i would call wasted effort. No-one gets a full picture of the scope, issues, internal links, or solutions; rather, details that may or may not be relevant once the whole thing is thought through are endlessly rehashed.
The purpose of the Scheme Topics mailing lists is to foster discussion that will lead to future SRFIs. It's important to have somewhere to discuss these topics in depth before concrete proposals are ready.
As for a generalized pre-SRFI mailing list, it sounds like there isn't yet consensus on that.