Following the poorly-considered price changes on Udemy at the beginning of April, my Udemy earnings are about a quarter of earnings in the three months before the changes. I believe a big mistake was limiting course prices to $20-50 instead of $10-80 or even $100 (in other words, in line with books prices). I never participated in Udemy's kamikaze marketing, or in affiliate marketing, so limiting the maximum discount to 50% made no difference to me. Yet Udemy-driven sales have dried up nonetheless.
You might want to read "Growing Pains at Online Education Startup Udemy as Amazon Rumors Swirl"
Speaking of Udemy, the article ends: "It seems there’s no end to the funds pouring in to bankroll the company. But for instructors trying to make a living, it may be another story."
I still suspect the long-range future of online courses of this type will be on subscription services (LinkedIn bought primary practitioner Lynda.com, before Microsoft bought LinkedIn).
"The worst form of inequality is to try to make unequal things equal." -- Aristotle
"Always do right--this will gratify some and astonish the rest."Mark Twain
"A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away." Antoine de Saint-Exup'ery
"Not everything that can be counted counts, and not everything that counts can be counted." Albert Einstein
"Make everything as simple as possible, but not simpler." Albert Einstein