Yes! I assumed sorting by episode number was the same thing as this. Thanks for pointing out the difference! 
I agree that it would be great to have the option to sort by all three methods: episode number, air date, and intended order.
It would still be nice to have the default sort order method changed to air date (@justin?), and then essentially have this feature request be to add the other two sort methods as options.
ETA: grammar 
I remember looking into this before and determined it was a pretty involved change (due to how we cache the data) to support multiple orderings which is why I didn’t do it at the time. I agree it would be useful to have an additional option to use the air date.
We don’t currently save alternate ordering info from TVDB and I’m not sure we will. TVDB sometimes creates entirely new episodes for those alternate orders and that would very quickly fragment the data on Trakt. TMDB in comparison, has alternate ordering but it re-uses the same episodes from the original order.
Yes. Exactly. This happened for example here:
https://www.thetvdb.com/series/empresses-in-the-palace
I double-triple asked them; “so i have to create NEW episodes to add an Netflix order?”…
But sad to see that those episodes won’t get imported by Trakt, even if TVDb will add those to the API.
So could it be done with info from TMDB?
Back to @MxFlix 's request, could Up Next/Progress be shown in air date order as default? It does not seem like it would affect shows like Firefly negatively because air date is the same as the numbering order in place now.
I need to look into it again. It’s not a simple change since several places in Trakt use the data, so I need to make sure adjusting the sorting works ok everywhere.
If I could give more than one like, I would! Thanks for all your time & effort!
Thanks for looking into it! 
I wanted to check in, whether this is still something being worked on.
I have taken to sorting my Up Next by Release Date. For unwatched series, the “next up” episode is considered to be the first Special, which is generally later than most regular episodes, meaning in that Dashboard Next Up sorting, the show gets pushed further back than it should. [Yes, I could order by premiere date instead, but that would only help for the unwatched shows]