Krita might be Qt based, but it uses its own plugin system for loading and saving images. Like KDE's thumbnailers, there is a plugin which just uses QImage:
https://github.com/KDE/krita/tree/master/plugins/impex/bmp
And like KDE its capabilities is not done by querying the plugin, but using a fixed list of formats. With Krita this is done by using Qt's plugin metadata system which can only be changed on compile time:
"Id": "Krita BMP Import Filter",
...
"X-KDE-Import": "image/bmp,image/x-xpixmap,image/gif,image/x-xbitmap,image/webp",
...
"X-KDE-Extensions" : "bmp,gif,webp,xbm"
Notice how this is called the "BMP" plugin, but other random formats are added since Qt also support those. (Through WebP is actually in a separate package on Arch Linux, which might not be installed.)
I don't think we can fake it like with KDE, but it should be pretty trivial to copy the code and change those few lines if you can get the build to succeed.
Krita might be Qt based, but it uses its own plugin system for loading and saving images. Like KDE's thumbnailers, there is a plugin which just uses QImage:
https://github.com/KDE/krita/tree/master/plugins/impex/bmp
And like KDE its capabilities is not done by querying the plugin, but using a fixed list of formats. With Krita this is done by using Qt's plugin metadata system which can only be changed on compile time:
Notice how this is called the "BMP" plugin, but other random formats are added since Qt also support those. (Through WebP is actually in a separate package on Arch Linux, which might not be installed.)
I don't think we can fake it like with KDE, but it should be pretty trivial to copy the code and change those few lines if you can get the build to succeed.