Well I don't really think it matters that much if the people or our kids' kids' kids in the near future won't have the chance to mine. Coz then again it's just cryptocurrency anyway, and with an unhoardable coin like bitcoin per se, you can't expect anyone, not even now to earn so much bitcoin he can effectively become a ruler of the future world.
Someone, I see, has no pressing problems and is interested in possible problems with cryptocurrency in six generations of people, given the fact that it is generally accepted that a generation of people changes every twenty years. Moreover, none of us will ever know what will happen to the cryptocurrency by this time.
My advice is to live with the current problems and enjoy life. How much more will change in 120 years. Nobody can know what the cryptocurrency will be like by that time.