I would think available power in the equation is important, but a style of trash pump that would have a:
1. Powered cutting head on the intake to cut the plants fine enough to be pumped.
2. Mechanical articulated head of some kind. Much like an optical endoscope.
3. Potentially a camera on the head, but unlikely visibility would be any good during operation.
4. Water would vacuum up the cut plants though the pump.
5. Follow on filter/centrifuge to pull most water out after pump.
6. Further mulch the remainder for collection, drying, and disposal/mulching for gardens, etc.

Tracking where the head has been already to "mow" would be hard, as well as designing a head that didn't clog but tough enough to chew through sticks and other debris.