I hate to bring up a topic that has been posted so many times already, but as we've seen no real solutions, I want to keep this discussion going.
There's a serious bug in iCloud Keychain related to HomeKit. Some invisible misconfiguration with Keychain renders HomeKit (Home.app and related features of the framework) unusable for some iCloud accounts.
Developers have seen this manifest in the form of the "Error 77" or "iCloud data sync in progress" errors. Users simply get an unusable Home.app. As it stands, there are developers unable to work with HomeKit, and users unable to use it.
I've filed a bug report, rdar://27928426. For anyone else still having this problem, please file a duplicate report.
And as always, let us know about any workarounds you've found.