Then if libui supports libsdl as it does to gtk-3.0 it would be nice, as gtk-3.0 is still quite heavy for many embedded systems. libui is based on C, and it is

Then if libui supports libsdl as it does to gtk-3.0 it would be nice, as gtk-3.0 is still quite heavy for many embedded systems. libui is based on C, and it is not really suited to compete with the c++/java full GUIs on Desktops, so supporting libsdl will certainly expand its usage.