That’s unfortunate then.
@halla For Blender I have seen commercial plugins (e.g. Substance Painter or 3dIO’s UV Packer) being shipped with two separate installs. One is a dedicated executable as a C(++) file and the other being a plugin that serves as an interface between the two. Apparently, that would be a sufficient legal basis for Adobe’s lawyers to give green light for GPL integration.
Would something like that be appropriate for Krita? Mixbox as a stand-alone module and a downloadable plugin? It certainly isn’t as neat as an integrated version, but if it saves a lot of work and helps with performance, well, it’s an option.