Currently HAL only reports oss.type as mixer, pcm, midi, sequencer or unknown. For ALSA OTOH one gets capture or playback instead of pcm for type.
It would be very useful to know if a given OSS device supports capture and/or playback (e.g. a S/PDIF output device doesn't allow capture).
I suggest to leave oss.type as it is and add another key, e.g. oss.pcmtype which could store an int:
Playback = 1,
Capture = 2
so that most devices would show oss.pcmtype = 3.
I'm not 100% sure how this could be implemented, but for the ALSA-OSS layer at least you could reuse the information about the ALSA device for the OSS device. I have no idea about actual OSS drivers, though...