I think I get where you're coming from on this, but it's based on an incorrect assumption. If by a hack you mean using the law to encourage use rather than the way the law was design to prohibit use, that's not what happened. The only thing a cancellation does is take away some evidentiary benefits, not any fundamental trademark rights. Although there is some disagreement amongst legal scholars, most probably Pro-Football still owns a Redskins trademark and will be able to successfully prevent anyone else from using it. So to the extent you think this is a good ploy because it leverages the absence of exclusivity, it doesn't do that.