What I'm missing in the proposal is support for user account stuff.
I.e. the stuff you get on the YT page when you're logged in: subscription updates, recommendations, friend activity.
For this, of course, one would need to provide the login credentials to your addon.
Its planned, although I haven't figured out yet how to do it in a secure and good way. The main problem here is that all requests to youtube go through a PHP proxy script. It's a bridge between the YouTube API and my YouTube addon. This is required because there is no YouTube API for C (the programming language this is programmed in) and to speed up the querying (e.g. about 20 HTTP queries are required to get a list of video files during browsing, this is very slow from your home WDTV, but no problem when you launch 20 parallel queries from a big ass web server).
PHP is not one of my primary programming language and I see it more as a necessary evil, therefore my proxy scripts probably have some vulnerabilities in them that could be used to get information like credentials when someone really wants to. And the communication from WDTV <-> Proxy <-> YouTube is not encrypted, so at any step the credentials could be spoofed.
There may also be problems with violating the YouTube API contract, not sure if it was YouTube, but a lot of other sites have a clause that prohibits storing and transmission from credentials to any third party service, kind of like the one the credit card companies have with they credit card number and security key.
So yes, when I have a plan how to do it in a secure way without passing the credentials through the proxy it can and will be integrated.