Core contributing is volunteer work, so they're motivated to make the improvements that they want--typically incremental improvements.

But it's better to risk boldness than triviality. The same community that's been working on something for a decade isn't just going to change--they're comfortable. We need new blood, new energy, and new ideas. Hopefully the new lead devs make a difference, but I don't know if that'll be enough.

To get more new blood working on WP we'd need to make it cool to work on again. The API stuff is cool, but we'd also need to push for other new things like HHVM. Not because it'll fundamentally change WP, but because it's something the people this community needs can get excited about. We need to make WP exciting to work on again to attract that kind of talent. Think working at Google/Facebook/Twitter vs. working at IBM/Microsoft.

The new folks don't need to be lead devs, they'll inspire the community just by hacking on stuff and building new things. Innovation and excitement are contagious.

Then we'd need to do a better job of showcasing the cool stuff people are building on WP to attract more people who want to do the same. Maybe get some evangelists out into the startup communities. Maybe put together a RFS (request for startups, i.e. https://www.ycombinator.com/rfs/) with a WordPress X prize. We need to cultivate innovation if we want to see it grow.