I am relatively certain that people will be rebuilding old Detroit and Cummins diesel engines in heavy equipment for at least the next 50 years, if not 100.

I have been surprised at how much 40V/80V electric systems are cutting into what was traditionally two-stroke light engines for string trimmers and mowers. The batteries are expensive though, and I don't know how many you'd need to have in rotation to be able to keep one fully charged and ready to go under continuous usage.