I see no reason to mandate anything before the FAA does. OEM and aftermarket will do little without clear guidance from the FAA.
As shown by all of the committees and studies currently underway by the FAA et al, who knows by 2020 what will happen. The MLAT stuff is a good indication of another system trying to get this to work.
It is obvious all of the short comings, so why jump in before it is sorted, especially if the OEM or aftermarket suppliers do not have a product available.