The API connectivity you speak is very doable in WordPress (take a look at Kickpress which turns WordPress into an API, or the JSON api plugin). I think you're on the ball in terms of the importance of a more connective experience.
WordPress is incredibly flexible and every day use-cases where people would have said 'WordPress is not the right tool for this job' people are starting to say 'actually WordPress can do this'. (Checkout projects like wp types/pods/buddypress/p2 etc)
I'd love to see more innovation going into WordPress. Right now I think it could be made a lot easier to use for beginners. I'm not really keen on the backend in that respects. Personally, I'm making tools that will make for smarter themes and more personable apps for WordPress.
There's also lots of blogging platforms that take a more minimalist approach if that's the direction you want to go in. Then you have to contend with established platforms like tumblr and posterous. And that market is also cornered by services like google plus and facebook which tap right into social networks which is very attractive to users craving connectivity with their network.
Last but not least, I'm assuming you'd want to develop something that makes money. In that case you need to really figure out a product that people will pay for. Personally, if I had to do that, I'd pick a niche I understand
Themeforce for example built a saas using WordPress( rather than building something from scratch) as the platform for restaurant owners. It's very customized so most people of their clients might not even realize it's WordPress and frankly it wouldn't matter to them either. I think their example is a great lesson: most endusers aren't going to care that much about the tool, they are going to care what results it gives them, the cost and how easy it is to use.
Right now I don't think your USP as it's coming across at the moment is exciting, new or radical. 2cts