There are two ways to use a handle to help to achieve maximum torque: sitting on the seat and pulling up; and standing on the pedals and pulling up.
For both of these functions, you need to be able to apply maximum upward force to the handle. You are effectivwely pulling yourself down onto the pedal.
If you are pulling up on the handle, the muscle action relating to the pulling up is similar to the muscle action you would use if lifting a very heavy single-handed dumb bell, or a bucket of water: you want to keep your hand (and the centre of mass of the weight you are lifting) close to your body.
For this purpose, a handle that is just in front of your crotch is about right. A good place to mount such a handle is, er… on the front of your seat.
If you do more standing up than sitting down, there is an argument for having a handle which is a bit further forward, so that you can allow the seat to fall back a little way so it isn’t in the way. However, it is not a good argument, because the pressure of the sides of the seat against the insides of your thighs helps with steering, balance, and general ‘feedback’ from the unicycle.
If the handle was so far in front of the seat that when you held it in the right position for maximum torque, the seat was way back out of the way, then you would need to divert effort and skill into maintaining the lateral stability of the unicycle - a bit like when you’re riding seat out in front.
So, for maximum torque, the handle should definitely be just a short distance in front of the seat.
How should it get there? Bolting it to the seat seams obvious. A stronger structure could be made by attaching it to a lower point and triangulating it, but at the expense of additional weight.
Of course, you don’t always use a handle for maximum torque. On rough or difficult patches, a light touch on the handle gives an increased feel for what the wheel is doing. It gives you that edge when coping with a series of unseen or difficult to read hazards. The ideal position for a handle doing this is also just in front of the seat because you need small movements of the handle to give you the feedback (a longer handle will move further) and you may need to stand up suddenly to apply torque.
So that leaves only the option of a handle for supporting the rider’s upper body when (s)he is riding long distance and needs streamlining - or simply to take some weight off the posterior.
Such a handle will only need to take a small amount of weight, although it will need to be robust in the event of a crash. A handle mounted on or just below the seat seems the best answer. This offers the shortest route from the uni to the handle, so lightest weight.
A handle up there in front like a set of bicycle bars would be no use at all for any of the things that you use a unicycle handle for.
Also, you will normally need a single handle, not a double one. especially when working hard up or down hill, you need one hand free for balance.
So, nice try but no cigar. Nevertheless, it is good to explore these ideas. A good rule for such explorations is keep it simple. The current design (Reeder handle or similar) is simple.