Yea, glue et al doesn't take video into account - tested that last year. While you wait for the cache/proxy file feature, you could almost as quickly render a low-res version in handbrake or ffmpeg, then just F2 > item source and swap between high and low res files - this makes more sense when your editing phase takes some time to complete. In reality, proxy files are an automated version of the same process aka both methods require the render time of the low-res file.
If you edit and have lots of splits in the video item, then renaming the video files themselves is probably faster than changing all those item sources if those have to be changed 1 by 1 in reaper.
EDIT: Looks like changing item source will do all items at once.