As a stopgap measure, I think having the choice to make scripts not continue until the video finishes is GREAT... though in theory, I suppose if the media player hangs/crashes (as WMP or QT often does!) it might mess things up. Still, a choice of 'playBackgroundVideo' (as it now works) or 'playVideo' (script pauses until the video finishes) would be a good solution for now without the troublesome workload of adding proper video support to SS, IMO.
As for future support, as much as I don't like limited video type support, I think for SS it would be a case of "any support is better than no support". Ideally, I'd want .mp4, .wmv and .avi (in that order) as the supported files, but that is likely a massive headache, I know. As much as I hate Apple, they seem to survive just fine with .mp4 only on their devices!
Also, having just one format supported would mean script creators having to convert videos to that format first, but given how few actually use video, I think that's okay. It would also possibly encourage using only short clips and keeping file sizes low.
Again, for me it's about having options.