Some cable/satellite providers mention the ability, provided by their set-top-boxes, to pause a video and continue watching in another room. I, for one, would find it very useful to be able to do this with PlayOn. It would also allow a second video to start loading for a second device while one is already playing and then switch to that preloaded video without having to change devices.
Do you do any device-specific transcoding? That would make this more difficult to implement.