It would be quite hard. Even if the Salic law wasn't institutionalized at this time, its principes were still existing : after all it seemed natural that the crown would have been transmited to a man as it was always the case.
Furthermore Joan was minor, with an illegitimacy suspicion around its birth...
Let's the the Valois couldn't do it because of an earlier POD (death? vilainy? war?) and maybe it could be considered as a serious choice, critically if the closer are only the Plantagenets.
For the consequences, i would say nothing regarding direct consequences...But if the Etats Generaux acknowledge the principe of woman acession to the crown, it could butterly the 100 years war at least as we know it.
But really, it would necessit an earlier extinction of Valois before, and it's hard to do.