Interesting read. I believe there is at least one thread in the UA forum on WilMA. While the concept makes sense, my resistance to this and similar processes is overhead space. With UA and other airlines tacitly allowing 2-3 carry-ons (remember that purses, camera bags, etc. each count as a carry-on) and some passengers who board early putting two or more of their carry-ons in the overhead bins, the last passengers to board may find all of the proximate overhead space taken.

If the carriers were to address the carry-on issues, I think they would find some additional efficiencies in the board process. There is no solution which will please everyone, particularly those who refused to be "inconvenienced" by checking baggage. However, improving the delivery times to the luggage carousels and reducing the number of bags which miss their connection would be big steps forward.

As a more drastic step, the airlines could issue one "overhead bin baggage tag" at check in (maybe 2 for those in F where there was extra space) to be attached to the item the pax intends to stow overhead. Any items placed overhead without one of these tags could be spotted easily and removed by the FAs if space was needed, so that those in the order last to board had a better shot at proximate overhead space.