I have two problems with this (admittedly fun) idea, both of which being the gasses needed to suspend the vehicles. One, hydrogen, the most effective of the two options, is extremely flammable (see Hindenburg). Two, Helium, is rare, nonrenewable, and invaluable in scientific equipment (such as FMRI machines and particle accelerators). While one could potentially make helium through the modification of nuclear (fission) reactors, that would massively increase the price (in both market and labor power terms), making it infeasible for transit after running out / low on natural helium deposits.