of the brassicas i planted very late, the curly kale is romping away, the cavolo nero is perfectly fine, and the PSB will just sit there I think.
in a way you've almost got nothing to lose, except for perhaps messing up any rotation you use, or encouraging brassica diseases, for no good reason (if they come to nothing)
you're probably in the hands of the weather also- you'll have a better chance of getting something it the autumn is warm and wet