The ultimate sanction - withdrawing the right to go in field service - is unprecedented as far as I (and other elders who I've asked) can tell.
I totally agree. Withdrawing the right to be a publisher is unprecedented to me and in the past has only been reserved for persons who were disfellowshipped. Witnessing is what defines the individual as a JW. This sanction is like a shadow judicial action that fits somewhere between a disfellowshipping and a marking...without even a judicial committee meeting or chance to appeal.
Also, I can't see how they can't follow this up with another letter at a later date for clarification. This is reminiscent of the confusion behind the "no oral sex" thing years ago.