One thing I think would be very nice if could be added is some kind of alternation when it comes to the boarding and deboarding sound. Especially when it comes to the time of day.
I'm just preparing a flight from ESSA-EGPH in real time meaning 4:45 PM local time in Sweden and then it feels a bit odd when you hear your cabin crew welcoming the PAX by saying 'Good morning, welcome aboard'... A more proper way to greet the PAX this time of day would of course be something like 'Good afternoon, welcome a board'.
3 sets of boarding/deboarding sounds would do it I guess, one for 'Good morning', one for good afternoon and one for good evening. Guess it wouldn't be too hard to find out the local time in the sim to know what sounds set should be triggered.
Then imagine if the sound sets could also be based on good/bad weather at the origin meaning the cabin crew could say something like "Good morning, what a lovely weather we have today" or "Good evening, nasty weather but you're most welcome aboard"
To me that would add a lot to the immersion factor!