I think there’ll still be a market for 2.79 (and earlier) tutorials. Keep in mind that unlike other 3D software, Blender’s earlier versions are available in perpetuity and a lot of people will delay adopting 2.80 until they know it well enough to use in production or (at least) feel comfortable with it.
When 2.5 was released, people continued to do 2.49 tutorials for quite a while afterwards. In fact, I’ve seen questions asked about 2.49 as recently as six to eight months ago.
As long as the version is identified at the beginning of each tutorial so the student doesn’t feel misled, I think you’ll be fine.
