I have not tried anything like that nor do I need to. I have all of the work 1 person needs to stay more than busy. The spider excavator is a fall back in case I get run out of my normal work, which I do not see happening before I retire out.
I like the concept of the remote control vehicles for safety on those steep slopes. I don't think that they have enough power for anything other than re-clearing work with grasses and very light brush. My experience is that anything over 20-30 degrees make steering difficult and complicates the job. I have been over 45 degrees a couple of times when traction allowed it. At those slopes, there is almost no steering possible because if you start to slide sideways, you lose all control. Next phase after that is a potential roll over, situation stuck and/or machine damage. A roll over with an RC vehicle would be a lot less stressful but could still be very expensive.
Because I work alone, I am always trying to be as time/money efficient as possible. I don't worry about re-clears that need a smaller machine, I don't work partial day jobs unless I get paid for the entire day, I try to spend my customer's money wisely and give them advice if I can not be cost effective for them. I don't see an RC machine in my future as it would/could not demand the rates that I get with my larger machines. For a big operation with lots of employees, an RC machine could make perfect sense but not for me. Unless they made them big enough to work 16" diameter trees or larger, there is no way I would generate an interest unless my business model was different.
As far as flail vs drum, I would NEVER own another flail mower unless I only wanted to cut grass. I started out with a Brown Brontosaurus flail mower. I got really skilled in my welding and gouging as I was forever chasing out cracks and rewelding the flail axle bushings in the rotor. It could not handle the size material that they advertised, without damage. I was forever welding bushings, replacing shafts, replacing broken knives, sharpening or rebuilding. When I made a new fixed tooth rotor for that head (using Fecon teeth), my world changed and productivity skyrocketed. I was getting nearly 40x energy transfer per tooth strike vs flail cutter. I no longer had size limitations as long as I had the time. Unless it is grass or saplings under 1" diameter, I have no use for a flail cutter.