A partner and I launched a free guitar web-based app: https://fretastic.com earlire this year.
We currently have over 15,000 members, and average around 450 visitors a day.
One of the biggest music theory channels (Signals Music Studio) covered it, which drove a lot of members.
I'm thinking of 2 possible ways to monetize this site:
(1) Hire a guitarist to create a course on how to use the site to learn guitar
and/or:
(2) Lock certain features (like the dynamic backing tracks), and offer them all under a premium subscription model for something like $9-10 a month.
Thoughts?
From my perspective, this is an excellent idea. Many people are interested in learning to play a musical instrument, especially on a guitar. So I am sure this app will have demand. Honesty as a music school teacher, I worked a bit with the guys from https://middermusic.com/best-online-guitar-lessons/ ,and seeing from inside how this industry works made me understood that this idea is not that bad. Who knows, maybe someday I will create my website for learning musical instruments.
You could test both 1) and 2) with a minimum viable product
Hope this helped.