Honestly, Scirra wouldn't even have to work too hard to make C3 even more functional since all of Rex's Addons are so great and well working! So i really would love to see some of his stuff being "officialized" and coming as a Standard Addon to C3
It is actually a great deal of work to contract out development work to third parties, involving communication, negotiation, writing out a spec, development, testing, and then long-term maintenance. If the plugin developer then disappears (which I believe has already happened anyway) then we are left maintaining somebody else's code, which can be much more difficult and leave users frustrated as to why bugs aren't being fixed or improvements aren't being made. Finally the whole purpose of the SDK is to allow development to happen without our involvement, so getting ourselves involved defeats the purpose of the SDK. If you feel any essential features are missing as official addons, you can suggest them on this site.