Currently they bring their own fuel to worksites. What happens when there's no outlet for them to plug into? There are large numbers of landscaping scenarios where this will be the case. Do they bring a diesel generator?

All of my yard tools, including my lawnmower, are electric. For reasons of both cost and power, I went with corded rather than battery powered. Battery tech is constantly improving and maybe at some point it will get to the point where it is viable for a yard like mine but for people who are doing a large number of properties per day, it's going to be quite a while.

Seems like the better interim solution would be making the small engines used by these tools emit less. This would of course increase the complexity and cost but seems like a better tradeoff than extension cords with large voltage drops, diesel generators, or lugging around half a dozen times more batteries than devices.