A couple of thoughts. If one were looking to upgrade to this, I would say for 99% of the TTs out there, it will not work.
#1 Solid axles tie the spindles together. As the wheels are offset to the leaf springs and the axle's mounting point, the axle tubes keep the enormous lateral force in check. The highly engineered, low margin frames we all love to hate would not work without extensive modifications that likely would interfere with whatever existing hardware/equipment that is between the frames. The independent wheel's offset position relative to its mounting position would make short work of any frame not substantially reinforced.
#2 As they are fully independent, the wheels would not benefit from the common linkage that allows the tandems of traditional axles to equalize on uneven terrain. This means that the trailer must be perfectly leveled at all times. If not, one wheel and swing arm assembly would see significantly more loads than the other. This would further compound the the frame reinforcement considerations that would have to be made.
