I have courses on Udemy, my own site and elsewhere. I don't think DTube will disrupt at the present moment.
Most courses take quite a while before it gets traction. Courses can be sold for a long time, sometimes several years, and by refreshing content. A 1 week payout is just too short.
The student experience is better on purpose built sites.
RE: DTube: The UDEMY Killer? Steem Opps for Edupreneurs