I can't help on whether or not it would work, but I'm really curious what you come up with here because I've had the same thoughts for my 4100. My problem has been, every time I try to design something similar to those carts, the expense of the unit, rails and fence along with the resale value of the Bosch is way more than just buying a hybrid type saw. I don't want to put $800 into a 'workaround' if I could just something made correctly for the same price.
OTOH, I actually use my 4100 out of the basement shop on occasion, so the 300lbs+ hyrbid is not a real option. Would your design allow the saw to be removed from the cart, or do you intend for it to stay fixed in place?