SageTV is dead, I'm afraid. The team is likely working on GoogleTV, but I kind of think Google is done with that segment. Online streaming is their thing, and it's the future of TV anyway.
It's US only now, but they said they were working to add more countries as soon as possible.
This is an interesting device but the bad news is that it's completely locked down by Google.
Not really sure what you mean by that. You can control it with any supported platform (iOS, Android, OSX, or Windows) through apps or through Chrome. Services need to add support, but there's an open API so any service can add Chromecast support if they want to.
And, of course, it's designed to be used with US services so it's also designed to be useless anywhere else.
Again, not really sure what you mean by this. Netflix, Youtube, and Google Play Movies all work just fine here in Canada. Obviously Chrome works here too. And any Canadian service can add support, if they want to.
That's probably because Google is planning to make money from ad services and sales.
I'm sure that's part of it. They can make sure that the YouTube ads still get shown, and they can encourage you to use Google Play Movies/Music, but I see this as a different play for them. For one, people using this dongle aren't using an Apple TV or an Xbox, which keeps them from being sucked into one of those ecosystems. For another, it encourages people to use Chrome as their web browser. I think those two are both a bigger deal.