Hi Mark
I don't have any particular plans to do any of these things - but some other people have been talking about something similar I think - try searching the forums for video.
Did just want to warn you that quite a lot of what you want to achieve with video wouldn't work on an iPhone (and possibly other phones) due to the way that it displays video in a separate player and not inline in the page.
There's a remote possibility you could do something by playing back video inside a canvas object, but that's pretty bleeding-edge stuff, I wouldn't want to bank on it working out!!
The contrib-media component currently uses MediaElement as a player - so we're a bit tied into the capabilities (and bugs!) of that. I think many people would quite like to replace it with something better, but it's not a particularly easy change to make once you get into it.
You can have the video component only mark as completed once the video is watched all the way to the end if that's what you mean by 'activity completion'?