As much as I like Blaze...probably not. Even before considering Blaze herself, the Sonic series has already done a lot to poison its own reputation, and mascot platformers are not exactly the "in" thing anymore. I'd be surprised if any Sonic character could carry a spinoff series as things currently stand. And again, I like Blaze, but she doesn't really set herself apart from Sonic much. Her gameplay is the same kind of high-speed acrobatics, her villain (regardless of which you pick) is a variant of Eggman, she's got her own set of magic rocks that can grant her a powered-up form. This works pretty well within the Sonic series where you can leverage the fact that she's basically parallel-Sonic, but if she got her own separate series it could end up feeling pretty redundant. They could make up entirely new stuff for her games, of course, but then you're rolling the dice on new ideas, not really making use of what Blaze already offers.
If they felt they could get away with a Blaze spinoff I'd still absolutely like to see it, though.