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It's quite common. Here are Richard Stallman's own words: "I've considered selling exceptions acceptable since the 1990s, and on occasion I've suggested it to companies. Sometimes this approach has made it possible for important programs to become free software." and "I consider selling exceptions an acceptable thing for a company to do, and I will suggest it where appropriate as a way to get programs freed." and more. The whole article is worth a read: https://www.gnu.org/philosophy/selling-exceptions.en.html

Qt famously is dual commercial/LGPL licensed. And while a commercial offering does go against the FSF’s ideals, it’s a necessary evil in some circumstances.

The FSF party line is that it isn’t anti commercial and the GPL is copyleft, not viral.

But you know…

But dual licensing has been around for decades and I’ve never heard them oppose it.

In practice here, no commercial licensee will want to maintain a fork. All improvements are in the OSS version available to any GPLed software.