Doesn't gmail already allow me to do much of this without having to trust another company with all my email content. Plus nothing to download as its a iphone optimized web app and nothing to pay in the future(unlike the proposed $3.99 monthly fee).
That being said, I'm a big fan of Gmail (and worked on it myself way back in the day ...)
At first glance it seems like you have a product that could be interesting only to Apple, if they can't easily add the functionality themlselves and the build vs. buy math works out.
because you already gave up all your privacy to google and have none left to spare?