Just as industry has warmed up to GPL3, it has slowly begun to accept AGPL3 code. The acceptance has centered around two loci: MongoDB and dual licensing.
MongoDB was an early adopter of AGPL3, and it had two very important things going for it. First, MongoDB pioneered the “NoSQL” database. It was cheap, scalable and effective, and caught on like wildfire. Second, Mongo published guidance for how to comply with the AGPL, without compromising the proprietary rights in applications that used it. Mongo provided Apache 2.0-licensed connectors to interface with applications, and stated that using them would firewall the licensing of applications—almost like AGPL with a linking exception. Industry heaved a collective sigh of relief and changed its policies from “never use AGPL” to “never use AGPL except for MongoDB.”
This is a great illustration of the “estoppel” technique of open source licensing. Because open source licenses are standardized and used by many licensors, no one licensor has the right to say what the licenses mean—at least vis-à-vis all the others. However, any licensor releasing code under GPL can provide interpretational guidance for its own software. In law this is called a estoppel, which is like a waiver, a statement made unilaterally by one party to its own detriment, inviting others to rely on it. For example, if I release some software under a license like GPL, and make a public statement that I never intend to enforce my conditions under GPL, it would be foolish for me to sue someone for violating GPL. The court would read my statement and conclude that it was not fair for me to invite the world to violate my rights and then sue them. Such interpretational guidance is not unusual in open source licensing; it allows licensors to use standard licenses in non-standard situations, tweaking them slightly to fit.
The other use case for AGPL, perhaps ironically, was dual licensing. The dual licensing model was pioneered by MySQL, and consists of releasing software under a copyleft license, and offering an alternative proprietary license, for a fee, to those who did not want to comply with the copyleft conditions. Before 2008, the license of choice for the open source prong of dual licensing was GPL2. It imposed the most conditions of any standard open source license, so it had the most power to drive potential licensees toward proprietary license fees. But AGPL added a new and significant condition, so it is now the favorite for dual licensing. In other words, in dual licensing, the scariest license wins.