For the record, I've pulled around my 5x10 trailer with a yard or so of mulch on my bucket and I didn't like it very much. I felt out of balance when pulling it over any undulations.
I would shove a boat around, like, a few feet with this type of rig, but as the past owner of a 5,000# 22' Bayliner, I can tell you that isn't a light thing. Not tongue load, mind you...I have no doubts a BX can handle that. It's the other 2.5 tons. Putting that type of load on the front lip of a bucket hanging way out there in space? Scares the crap out of me. Simple COG thing.
But my world has hills and bumps. On the flat, I guess it'd be OK. God bless any fool that tried to hold a boat on a launch ramp with a ball in the bucket.