Startup cli flag to temp disable audio device use?

This would be convenient for development.

I guess this would also go hand in hand (i.e. require) the ability to load a track to a deck when all output device dropdowns are set to None(?)

That is already possible.

When all devices are set to None, and I try to load a track, the deck gets the Loading... change, but nothing happens after that. If I go back into the options and select a device, then the tracks I've tried to load actually get loaded to their deck.

2.3 beta, r6820-1 (built yesterday iirc, quickly with ccache now!)

I cannot confirm on Ubuntu Bionic that the track is not loaded with no Sound Hardware configured.
On which OS are you?

Well, this is confusing, I'm now able to load a track to a deck with None for all, either after going back to that or starting with.

Ugh *shakes fist at intermittent issues*

The only thing I think is different now is that the dialog that opens on start with no devices selected now has just three buttons, including a Continue, where as before there were 4 and I had to select Reconfigure and then OK (with all None) to proceed. Maybe that's something else, maybe the "fix" was related to https://mixxx.zulipchat.com/#narrow/stream/113295-controller-mapping/topic/Reloop.20Beatmix.204.2FXML.20confusion/near/214128764

I have had this problem in the past before though. I'll see what steps to reproduce if it happens again in future.

Still, having a flag to bypass any valid device settings (to avoid having to switch to None to release a device, and then revert that after doing dev things) would be handy.

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/10174