"Or at least until cold weather as you're right about not enough time to get established this fall. Seed will over-winter very well (it managed
on its own for years w/o us at all, so that's nothing abnormal) and particularly where one gets some snow and freeze/thaw cycles it works to get it in good contact w/ the ground and it's there all ready for spring... "
That's an interesting question, which comes down to what germination rate one would get next spring from seed that was planted in early winter, when it' too cold to germinate. You'd have to compare that to the germination rate from the same seed planted in spring. I would expect to see that the germinatin rate is substantially higher for the seed planted in the spring. You're right many seeds are designed by nature to make it through the winter. But even then, it's a statistical thing. Enough obviously must make it to keep the species going, but that doesn't mean that given the choice of spring planting, that spring planting wouldn't be substantially better.
And I'm not sure about typical grass seed, like fescue or blue grass. I would think in nature, most of these would form seed heads in summer and then germinate and establish in the fall? And I would think a substantial portion of any seeds left for months on the surface would succumb to wash out, animals, rot, etc.
Bottom line, I would go with the conventional approach. In Chicago, that would be seeding in Sept, which would be best or waiting until early Spring.