The obvious solution is to use something like the hybrid Ford F-150, which will only run the engine as-needed while still providing continuous 7.2kW power for battery charging or directly powering tools.
That's going to be a tough sell for landscapers currently getting by with a 25 year old F150. If the state is forcing these costs onto working people like this, they should also subsidize the cost to get newer legal equipment. The state of california already offers funding for wealthy people to buy Teslas, they should do something for day laborers too.
Landscapers currently getting by with a 25 year old F150 can continue to also get by with their existing tools. They won't need a new F-150 to serve as a generator until they are well into the process of retiring their gas-powered tools in favor of electric tools. And there will even be a grace period of several years where they can start migrating to electric tools and buy a separate generator. Because these rules are about what's legal to sell new, no what's legal to have and use.
(Also, based on CARB's definition of "Small Off-Road Engines" which is what the law applies to, diesel generators of any size will not be affected.)