Best way of presenting both 720p and 1080p screencasts
Generally speaking shooting in 1080p and scaling it down to 720p is not a problem with cameras as I do this all the time and it looks just fine. When I do this I may also be mixing 1080p and 720p raw images, and I always scale to the lowest resolution. When I render a 1080p I will generally render a 720p version as an answer print to view before committing the final cut to a 1080p render. I say this with caution because I have not worked with screencasts or using screen motion capture software.

However, shooting in 720p and trying to make it into 1080p is a losing battle because then you are asking software to make up for pixels that do not exist. You can try it, but I don't think you will like it unless someone makes a software product something like Twixtor that adds frames needed for extra slow motion shots.