I agree but I'm not saying put some blues chords and blues melody together over a rock beat and a walking bass line and say, "well this is blues". When you mix elements of different genres and styles, it does create something that is no longer one clear genre. I'm talking about other elements like form and structure, which can be manipulated without effecting what you distinquish as genres. The beautiful thing about form is it's predictability. In a typical ABA form; the song form verse, chorus, verse. After the chorus, you naturally expect the music to resort back to the verse again. It's been done so many times that it only seems natural. But you could throw a bridge in there and the result would be ABCA. Which is not uncommon either, and if done well it still will sound like a natural progression.

This can be summed down to everything in music. The V chord doesn't have to go I, it can take a detour. Or with the 12-bar blues, you could add an extra 2 measures at the end just to sing "I'm your honeybee". The question you have to ask yourself is does the music continue to flow naturally. Does adding an extra chord sound progressive or is it a thorn in your side?

Defining a genre is hard to do in words, but I think everyone knows blues just by it's characteristics. Like you hear a tune and you go that's a cool rock song, you can clearly do so without saying well the form is this, the chords are this, and the rhythm is that so it must be a rock song. You just know by the sound of it. You can do the same with any style, even when you write a blues tune. If it's blues by distinction; form, structure, chords can be bend broken and manipulated and people will still call it blues. Of course doing so is always a gamble (the more you change the harder it is to remain 'blues'), but if it's done well. Meaning it is predictable, keeps the music flowing, and has a typical blues characteristic. Blues players will probably accept it, especially if it's something cool. Re-invention or just throwing a nice spice on something is always nice.

Remember it's not always the musicians who name genre's. Nirvana didn't come out and say, "we're grunge". You can also look at it, if this did happen and you invented a new genre. You'll get a lot more recognition doing so. Me, I'd want to be associated with creating a new genre over doing a really good (blank) song anyday. Just hopefully the new genre would be well accepted.