That's just how Gentoo operates - Gentoo is about choice. That often means that we put effort into supporting choices that many users will not make, such as allowing users to use systemd as their init system, or creating a udev fork.
Is eudev officially part of Gentoo? Yes. Does that mean it will ever be the default replacement for udev? Not necessarily.
Eudev does have the official support of Gentoo, but that really amounts to little more than some hosting. They could of course apply for financial support like any other Gentoo project, but such requests are rare, and honestly I'm not sure what it would be needed for here.
Gentoo is a volunteer organization. If somebody wants to work on something, they can. If others think that what they're working on is dumb, they can work on something else. As long as nobody is breaking the law we're fine with that.