We already have robot grass trimmers and they work pretty well. Why would you want a crude, inefficient, facsimile of a human push or power an inefficient form of mowing the lawn?
I can envision a future where people have a humanoid trimming a small backyard but at the same time the maintenance of e.g. a golf course would be done by dedicated robots.
EDIT: my point is that just like smartphones replaced a number of specialised devices for most people, a humanoid robot could do the same, by virtue of being a general purpose machine
I want a pretty good facsimile that can cook, clean, mow, carry stuff around the yard.
I want this much more than a robot lawnmower + robot vaccuum + plus other single purpose automatons.