I made changes to the old Dolphin  YouTube iframe code to include a whitelist of allowable video sources.  I basically left the Dolphin iframe in place so that mine would not get changed during any upgrades.  This would be a nice addition to Cheetah that would allow a white list to be developed, easily changed from the back end instead of editing the htmlpurifier iframe file when changes would be needed.  I added several video sources; vimeo, facebook, bit chute (really important one with the YouTube censorship), etc so that my members could post videos from more sources.  I posted my method of this on Boonex but of course a better solution than mine might be available now.  Basically it uses regex to look at the URL and if matched, then allows the iframe to be embedded.