If I remember right, the motion failed mainly because United voted against it. I assume they will vote against it again unless something has changed.
There's a little more to it than just classifying 401k contributions as duesable. If your airline had another retirement program (like a pension), the 401k contributions have always been included in dues. So, for FedEx and Alaska, there's no reason to vote against it because it won't change their calculations one bit.
If your airline has no retirement other than a 401k, then currently the amount you contribute is not subject to dues, but will be under the proposal. If I remember right, some of the airlines were inconsistent about how they handled this, with some airlines considering a B plan a retirement program and therefore having to pay dues on 401k contributions, and some did not consider it that way. I could be wrong on that, but that's what I seem to remember.
Under this proposal all will be unified, however, it would affect the regionals and the lower-tier national airlines without a B fund the most. That's why most of the regionals voted against it (except Mesaba for some reason, probably due to handwringing from the NWA MEC at the time.)