Canon based spin-off, i tried to say, like a spin-off game that is accepted as canon in the game story-line.
I understand what you said about a game evolving, and frankly, is an interesting way to build a franchise up. But i don't know if there is a formula or something, but not all games can be that way... sometimes it may work, sometimes it won't. Sadly for me, Star Fox is an example of experimenting in the wrong way, and then trying to go back but failing at it.
Sometimes games need to stay the same, just with one or 2 new things and variables. Like Zelda for example, the formula is the same year after year, but we all love each game, so is this, that fans still complain about Skyward Sword not being a real Zelda game. I think every game has an essence that developers should respect. You play Mario for fun, you play zelda for mistery and story, you play metroid for suspence and atmosphere, you play Star Fox for airships and non-stop action.
Well thats what i think, i don't want to sound like what i said is the absolute truth. It's just what i think. And i won't say that recent Star Fox games are crap, but certainly, i didn't like them, so... for me the franchise is dead and slowly rottening and we made this flash to express our opinion and for fun. x)