When it comes to using DLNA and playing local media, the situation of lossy audio support that endures with the Roku is a handicap for me.
Can a developer tell me: Is there any particular reason that 5.1 channel AAC can't decode to 5.1 PCM, or is this basically arbitrary? Just this minor change would make a significant difference to me. Considering the existence of a functional AAC decoder on the Roku, I can't conceive of why this can't be arranged.
Also, given its standardization by the IETF and demonstrable superiority in quality and licensing, will Opus codec support ever be a consideration?
I believe you mean lossless. Roku already supports lossy AC3, and it will pass lossy DTS via HDMI or optical to an AVR that supports those codecs. I can't explain why they won't permit passing all audio bitstreams via HDMI, but there's some potential of it being a licensing issue. Also can't explain why they won't support multi-channel AAC. One possible guess is that they are considering their typical user that just plugs the Roku into a TV, and don't want any issue with them playing something with unsupported audio. Remember that very few TVs can handle anything other than 5.1 Dolby or 2 channel PCM. My Samsung will also recognize DTS, but it changes the function and never changes it back with different audio. But I stopped using the TV for anything but OTA channels a long time ago.
Dan Roku Stick (3600), Ultra (4640), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.