Yes - DirectFB is used by embedded linux developers who want to use SDL2 on small boards - eg automotive, aeronautics, manufacturing etc etc . Below is the source code snippet from Buildroot - a widely used tool by embedded linux developers - for DirectFB in SDL2. If DirectFB is removed from SDL2, this code will have to change and it would impact use of SDL2 in the embedded linux community.
I personally depend on the SDL2 DirectFB video interface for my project. I have helped in migrating the SDL2 suite to Buildroot for embedded linux developers. I would prefer if DirectFB for SDL2 was not removed.
SDL2_DEPENDENCIES += directfb
SDL2_CONF_OPTS += --enable-video-directfb
SDL2_CONF_ENV = ac_cv_path_DIRECTFBCONFIG=$(STAGING_DIR)/usr/bin/directfb-config
SDL2_CONF_OPTS += --disable-video-directfb