Eugene,
Readline 8 is still in the experimental repository. Netlabs needs to move that to the release repository to be with Fluidsynth, so definitely report that. If you want you can add the experimental repository to ANPM, but be aware that some things there can be buggy or unfinished (beta), so tread carefully.
Once you get fluidsynth give KO Myung-Hun's KSoftSeq a try - it adds software MIDI playback from the WPS using soundfonts and works pretty well! Only editing is not supported (yet).
Regards,