I'm totally with you, just condensing similar threads and thoughts into here:
This I'll disagree with. There is not a better option out there if you want to manage all content in one place. TiVO DVR's metadata is complete garbage as is their lack of service integration, which makes it even more useless. TS4K+ has slightly better metadata and integration, but lack of low level controls (delete an episode or mark as watched!) makes it almost pointless. Google TV is pretty similar and the horrible nonsense that is a single row of shows/movies in order of reverse last added... ::shudder:: ATV still can't make an agreement with Netflix. Roku only will show things when they are new. Plex doesn't have anything for outside content.
That all said, being the best of this bunch is nothing to hang your hat on. Improvements are certainly needed, as you've summarized.
What I would really love would be if the Stream Link redirected and opened up the video inside the Channels Player. Then it would truly be seamless, would not require additional apps (use the browser versions), mean there is no need to worry if a service supports deep links or not, and remote control functions would always be the same. I am well aware of the terms of service of these companies about redirects, but I don't believe they are legally enforceable (and PlayOn certainly doesn't think so, either).