I can tell you it exists since I'm doing exactly what you describe: providing short sessions over Skype/shared-screens, on various topics including pure coding,

I can tell you it exists since I'm doing exactly what you describe: providing short sessions over Skype/shared-screens, on various topics including pure coding, freelancing, or ETL. I only do that on a lightweight volume (and I am paid for that since this year). I believe Avdi Grimm does something similar too. This is something I really enjoy doing, and I'm surprised that it's not more widespread.