I've been reading through more articles.
This article discusses (in a fn) whether GPL is a contract or a unilateral licence. The GPL version of the "licence to all recipients" provision doesn't use the word "offer". Rather, it says the recipient "automatically receives a licence". Brian W. Carver, Share and Share Alike: Understanding and Enforcing Open Source and Free Software Licenses, 20 BERKELEY TECH. L.J. 443 (2005).
This article quotes the GPL provision and then says (p 633) "So if all goes as provided in the GPL, everyone who receives a copy or modified version of the software also receives a license and her use of the software is subject to the license terms" - but without actually confirming whether or not all will go as is provided for. Molly Shaffer Van Houweling, Author Autonomy and Atomism in Copyright Law, 96 VA. L. REV. 549 (2010).
This paper is excellent in my view formed from a quick look through it - Molly Shaffer Van Houweling, The New Servitudes, 96 GEO. L.J. 885 (2008) - and discusses these issues directly. It articulates some of the reasons for my uncertainties - ie that these sorts of "automatic offers" are really a type of property right rather than a contractual matter. But I don't think it addresses the circumstance where the offeror resiles from the offer - its focus, rather, is on how the "automatic offer" makes the recipient bound by the same terms as the licensor imposed on the intermediate licensee.
Finally, this article actually discusses the exact issue: Lydia Pallas Loren, Building a Reliable Semicommons of Creative Works: Enforcement of
Creative Commons Licenses and Limited Abandonment of Copyright, 14 GEO. Mason L. REV. 271 (2007).
The following is from pp 313-4 (footnotes omitted):
Professor Merges argues that "for content to stay in the semicommons envisioned by the Creative Commons device, there must be an unbroken chain of privity of contract between each successive user of the content." The restriction that any reuse or distribution of the work contain the license, or a link to the license, is an attempt to bring all users who might encounter a copy of the work and subsequently use the work into privity with the copyright owner. The Creative Commons licenses also attempt to assure privity through clauses in section eight of the licenses, which state that each time a copy of the work or a derivative work is distributed, publicly performed, or digitally performed, the copyright owner "offers to the recipient a license to the Work on the same terms and conditions as . . . under this license." The use of a license attached to copies of a copyrighted work and the requirement that users reproduce that license on any subsequent copies as a means of trying to assure privity of contract is a strange and yet ubiquitous phenomenon in recent decades.
The practice of attaching licenses to each copy might be more accurately characterized as creating equitable servitudes instead of contract
rights. Are these really contract rights that are being created, or are they more accurately characterized as equitable servitudes? While equitable servitudes are applicable to real property, the possibility of creating such servitudes on chattels was presented almost a century ago but never fully embraced. Perhaps it is appropriate to say that the Creative Commons licenses attempt to create an equitable servitude that "runs with" the intangible work embodied in the tangible "chattel" copy. Characterizing these license conditions as equitable servitudes may, in fact, be a more accurate characterization.
The previous article - the one that I described as "excellent" - is a critique of the "equitable servitudes" analysis as being legally satisfactory.
At this point I'm happy to say that the proper analysis is not settled - but I feel somewhat vindicated that there is published work that is able to clearly articulate the uncertainty that I intuitively felt.
EDIT: I missed this one - Eli Greenbaum, The Non-Discrimination Principle in Open Source Licensing, 37 CARDOZO L. REV. 1297 (2016).
From pp 1341-2 (footnotes omitted):
under many open source licenses, each distribution of the licensed work results in a new license grant. The Creative Commons licenses, for example, provide that "[e]very recipient of the Licensed Material automatically receives an offer from the Licensor to exercise the Licensed Rights." Similarly, the GPL provides that "[e]ach time you convey a covered work, the recipient automatically receives a license from the original licensors, to run, modify and propagate that work, subject to this License." In other words, by releasing material under these licenses into the wild, the copyright holder begins making a series of license grants that she is powerless to stop. Each subsequent recipient of the material benefits from a new license . . .
But there is no explanation here of why
the licensor is powerless. So it doesn't erode my feeling of vindication.