Hi personaleu,
great suggestion for Google+ Hangouts! I'm sure Google will take it into account and implement Hangout session video recording > uploading to YouTube very soon.
Please note that you've posted suggestion about Google+ in the Google Chat Help forum. Feel free to share it in the Google+ Discuss forum: http://www.google.com/intl/en/+/learnmore/forum/ because this is where you'll have the best chance of receiving an attention to your suggestion.

Until then please feel free to use one of the screencast tools:
* Comparison of screencasting desktop software: http://en.wikipedia.org/wiki/Comparison_of_screencasting_software
* Comparison of online screen recording tools: http://www.labnol.org/software/compare-online-screen-recording-tools/9454/

Cheers,
Aygul