Yes the GPL is revocable.

[mikeeusa2@firemail.cc]

> However, nonexclusive licenses are revocable (meaning the copyright 
> owner can revoke the license at any time) in the absence of 
> consideration.
> https://www.dmlp.org/legal-guide/creating-written-contract-transfer-or-license-rights-under-copyright

> [...] The most plausible assumption is that a developer who releases
> code under the GPL may terminate GPL rights, probably at will.
> --David McGowan, Professor of Law, University of Minnesota Law School:

> p278 "Notice that in a copyright dispute over a bare license, the
> plaintiff will almost certainly be the copyright owner. If a licensee
> were foolish enough to sue to enforce the terms and conditions of the
> license, the licensor can simply revoke the bare license, thus ending
> the dispute. Remeber that a bare license in the absence of an interest
> is revocable."
> --Lawrence Rosen
> https://www.amazon.com/Open-Source-Licensing-Software-Intellectual/dp/013148787


> ("[N]onexclusive     licenses     are     revocable     absent     
> consideration.").  Where  consideration  is  present,  however,  the  
> license  is  irrevocable,  and  "[t]his  is  so  because  a  
> nonexclusive  license  supported  by  consideration  is  a  contract.  
> Lulirama  Ltd.  v.  Axcess  Broad.  Servs.,  Inc.,  128  F.3d  872,  
> 882  (5th  Cir.  1997);  see  also Carson v. Dynegy, Inc., 344 F.3d 
> 446, 451 (5th Cir. 2003).


> https://ir.lawnet.fordham.edu/cgi/viewcontent.cgi?article=1592&context=faculty_scholarship
> For the same reason, a licensee's commitment to use offered software in 
> a particular way cannot constitute consideration. Because the licensee 
> has no right prior to the license to use the software in any way, a 
> grant of only limited uses of it is merely a gift. The fact that the 
> giver could have been even more generous by granting use of the 
> software with no restrictions does not alter this conclusion. It is 
> still the case that the licensee has not given up anything. Only if the 
> licensee gives up some right, says contract law, will there be valid 
> consideration.


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Additionally if you dislike that method and prefer a different method 
explicitly stated by Congress:
By statutory law, an author can recover any copyrights signed away after 
(+-)30 years (US Copyright act).

The design of a program etc is a copyrightable aspect. RMS fixed this in 
form 30 years ago.

> https://www.copyright.gov/docs/203.html
> Termination of Transfers and Licenses Under 17 U.S.C. §203
> 
> Section 203 of the Copyright Act permits authors (or, if the authors 
> are not alive, their surviving spouses, children or grandchildren, or 
> executors, administrators, personal representatives or trustees) to 
> terminate grants of copyright assignments and licenses that were made 
> on or after January 1, 1978 when certain conditions have been met. 
> Notices of termination may be served no earlier than 25 years after the 
> execution of the grant or, if the grant covers the right of 
> publication, no earlier than 30 years after the execution of the grant 
> or 25 years after publication under the grant (whichever comes first). 
> However, termination of a grant cannot be effective until 35 years 
> after the execution of the grant or, if the grant covers the right of 
> publication, no earlier than 40 years after the execution of the grant 
> or 35 years after publication under the grant (whichever comes first).