The framework I mentioned (Firebreath) already provides an abstraction layer for those APIs. I agree iOS will be the hardest nut to crack, but since this is a long-term project I'm pretty sure we'll be able to work something out (either by Apple's blessing, by providing an HTML fallback mechanism or something else) when the time is right. Right now we're just trying to figure out if it is at all possible to create a better technology...
Why do you think that you'd throw out hardware acceleration? The latest Flash has hw accelerated video, for example, so not at all impossible. Advanced layout logic? Don't make me laugh... do you mean floats? Or inline-blocks? I've had my share of trouble using theme (I'm a web designer with many years of experience...). Layout is exactly one thing that we're trying to do better! And to use flexbox and all the other new layout stuff reliably you'll still have to wait a couple of years, I think. Then you'll probably still need to create a conventional layout for older clients for much time ahead...
And for the text rendering, there are plenty of open source libraries out there, we won't reinvent the universe from scratch just to make an apple pie.
As I said... the prototype will soon be available for anyone to try out so web designers and programmers will be able to play with it as a browser plug-in, this is not just some crazy random idea ;)
I dont think that's going to happen anytime soon.
But I agree that JavaScript is the way to go with this. The prize is not that high to justify such a steep adoption curve. I mean "make A as wide as B is high" can be accomplished in javascript today.
And again, we would love to hear about how we can market ourselves better, we are all ears!
C++ is also less cross-platform in this sense because to support multiple platforms, you will have to support compilation across target platforms and handle the variety of plugin APIs available for those platforms. And on iOS, your stuff won't work at all because it's Javascript or the highway if you want to run in Safari. (I guess you could ship your own browser on the App Store, but I suspect you'd run into rule hassles.) Maybe you could use Native Client, but in that case you will need to ship native client binaries for each CPU architecture and you'll only work inside Chrome.
Attempting to entirely supplant the browser's rendering engine with yours in a plugin is also a hopelessly shortsighted move. You'll be throwing out all the hardware acceleration and advanced layout logic provided by modern browsers. Just rendering text is complex enough to require multiple full-time salaried engineers, and you will have to bear that burden if you will ever be compatible with HTML/CSS, because international text is important.
Build a prototype using JavaScript, HTML, and Canvas/SVG where needed. Put it in front of people. Let web designers and programmers play with it. If they can play with it, they'll find reasons to love it. Once you have web designers and programmers who love your actual product, you have a path to success.