I think that media-libs/libsdl should not depend on media-libs/audiofile if the noaudio useflag is set. I know it's a little thing (so the priority), but I try to reduce dependencies to install a game server on my headless system and think it would be nicer without this lib.
done
I don't understand why libsdl depends on audiofile at all, even with sound enabled. ldd output for /usr/lib64/libSDL.so doesn't mention libaudiofile, and indeed there's no occurence of the words "audiofile", "libaudiofile" or "laudiofile" in the unpacked SDL-1.2.15 source. (Confirmed with grep -Fw.) This matters because audiofile is buggy: see https://blogs.gentoo.org/ago/2017/02/20/audiofile-multiple-ubsan-crashes/#utm_source=feed&utm_medium=feed&utm_campaign=feed