It feels a bit unnatural to have fly enabled when you switch into survival -- especially when you go to use your Elytra unknowingly. Perhaps make this configurable?

I'm quite confused. Why would you ever use /fly if not in survival/adventure?

Ah sorry about that, I'll try and clarify a bit better.

Basically what I've experienced is that switching to survival from creative or spectator (on version 0.16.1-mc1.17) leaves flight enabled for survival.

That behavior caught me off guard; I was expecting flight to be disabled as I hadn't previously enabled it in survival.

Going to confirm that i have been experiencing the same

Oh, that's exceedingly odd. Will look into this.

If all has gone well, this should be fixed by 0.16.2.