"This rule is being proposed under section 4213(a)(2) to make clear that use of 4044 rates, either as a standalone assumption or combined with funding interest assumptions represents a valid approach to selecting an interest rate assumption to determine withdrawal liability in all circumstances.... The proposed rule would specifically permit the use of an interest rate anywhere in the spectrum from 4044 rates alone to funding rates alone.... PBGC requests comments on whether the final rule should specify assumptions or methods other than interest assumptions ... The changes in this proposed rule would apply to the determination of withdrawal liability for employer withdrawals from multiemployer plans that occur on or after the effective date of the final rule. The proposed rule does not preclude the use of an interest rate assumption described in proposed Section 4213.11(b) to determine unfunded vested benefits before the effective date of the final rule."