I'm surprised the poll results are the way that they are. People like the idea of including the clause, but worry they'll be criticized for using it. For the record, I voted that I would not be worried about it.
Yoast and Gravity Forms come to mind as businesses that have stated on the record as saying they reserve the right to disable keys for misusing resources.
In the Gravity Forms terms and conditions, it states:
Rocketgenius, Inc. reserves the right, at any time, to modify or discontinue, temporarily or permanently, a support license with or without notice.
And here's a similar clause in Yoast's terms:
10.6. Without any liability to compensate the Customer Yoast reserves the right to disable updates and support in case of abuse and / or in the event the Customer is in violation of the preceding paragraph. This will not grant the Customer the right to a refund.
The clauses have nothing to do with restricting use of the code (that has already been downloaded), they're just reserving the right to terminate the associated services: support and updates and such.
Merely including the clause shouldn't be an invitation for criticism, but being a bit too gung-ho when it comes to "enforcement" could certainly be.
If it became clear that the GPL resellers were funneling their customer's support requests to you, or passing out their developer license keys, I don't think they'd get much sympathy from the WordPress community if their account was terminated by the original developer.
If a GPL reseller wasn't doing anything abusive (funneling support, sharing license keys, trademark infringement, etc.) and the original developer somehow discovered the mere "reselling" and subsequently terminated their account, that would be another story.
I can't imagine the GPL reseller getting much sympathy in that case either, but that debate would definitely be a bit more divisive.