I see still the recommended videos-section doesn´t deliver to your users liking; although the idea "Tighten the scope of the recommended videos list" is marked as completed.
As my title speaks, it would work wonders to use the CUMULATION of submitted searchs by a user connected with the cumulation of tags wich are related to the watched videos/photos in the users history.
Filter out the most often appearing tags and terms in a users search- and viewhistory each one by one, count them each, and chart the counts.
Best would even be to put them on a seperate php/html file for a user in his member-section and give him opportunity to delte and arrange the hirarchy of his liked terms.
Really, please do this! You could even improve it more to the better, but this alone would be an improvement of decades! ;)
Best wishes. Keep up the good work.