That's an interesting question that I have often wondered, and also wondered why there does not seem to be any software that does it. In principle it seems so simple given compressed formats like mpeg.
Take a very simple mpeg, I frames every 30 frames. For 30 fps (OK NTSC is 29.97 but we'll make it 30 to save my fingers typing it) take one second, 30 frames required. The mpeg algorithim would normally do the maths to produce 29 interframes. There is absolutely no reason it cannot calculate 59 interframes (more than common with the wmv format) to make 60 fps, or any other number for that matter.
In reality there are B and P frames so all you would be doing is making extra P frames. Not a big temporal interpolation (wow, did I really say that?).
Using the same method and playing back at 30fps you can make slo-mo that does not do some cranky version of 3:2 pulldown by mixing up fields of successive frames.
Starman*