Yeah, Rockbox ships as a GPLv2 licensed package, without the “or later” option for users to switch license at will. This has been all fine and dandy for a long time and Rockbox includes source from a busload of different other projects, licensed as GPLv2 and BSD etc.
GPLv2 and GPLv3 are not compatible. We cannot ship binaries built with a mix of these licenses.
So, we’re now starting to see the real-world effects of the GPLv3 license. Slowly some projects are going v3, and we (as in the Rockbox project) must remain with their older v2 sources until we take the jump (more or less forced) to v3 – only to then have the reversed situation as then we can’t use projects that are licensed strictly GPLv2 (without the “or later”)…
Sigh. The world is a complicated place.