With respect to the original proposal, the swap arrangements may involve more than one pension fund, and the swap guarantee may be partial, at a price that in normal times should compensate the Treasury for the risks it undertakes. In this case, it would be especially important to keep pension fund fees and other expenses low, as mentioned earlier.
One merit of the Modigliani proposal is that workers with similar characteristics would be granted similar rates of return on their savings. On fairness grounds, it seems disputable that workers with equal pension contributions and in equal in all other relevant respects should end up with very different retirement wealth, due to the evolution of financial markets.