Very simple suggestion if /fly auto is on, automatically put the player into fly mode upon logging in if /fly auto is off, don't. ezpz kthxbai -waffle
There's already a feature like this, and it's already in place. But overall, it would have to be added to essentials. Decently easy, but slightly complex.
just rewrite the code that evaluates if you are airborne when logging in to default return true then simply don't evaluate if toggle is active :3
What happens if someone is actually falling when they log in? It'll activate fly for them no matter what. @KHobbits would have the final say in adding it. I'd personally add a spot in playerdata, whether they logged out in the air or not, and if they had fly enabled then. And on login, they would be renabled accordingly.