From one armchair to another:

I think this idea is technically feasible, but have to wonder how much demand there would be. I agree with the placement of fasteners. I would probably set rivnuts into the inner tube, and countersink the outer tube (which would be best done into a thick wall, say 1/4in). 500mm of 3D printed tapered sleeve, well bonded onto the upper tube, should be easily able to carry the vertical load, leaving the mechanical fasteners to resist torsion only, so they needn’t be very big. The sleeves between the tubes would have to be carefully sized to fit well, not having any sealant or adhesive to fill the gaps. Some thought would have to be given to making a cable conduit tube separable too, but that shouldn’t be too difficult.