I wouldn't bank on people swapping ! I had a great seat once, loads of leg room on the outside of the aisle with a window just in front, you could stand up and look out of at will , near toilets but not too close. Sat next to very quiet people and so on.
My DH was in the middle aisles and in the middle of them iyswim, (we were separated as late checking in for some reason l cant remember) and had a lady sat next to him who was travelling alone. Neither of them could get up without having to disturb people.
I am petrified of taking off and landing and hang onto DH for dear life usually.
DH asked lady very politely if she would mind swapping with me and explained why and also that l had a very good seat for all reasons stated above.
I was in a right state and even thought of asking to get off
. She flatly refused, no reason - and yes l know she was under no obligation to give one etc.
Only a lovely air hostess managed to calm me down a bit and l survived take off obviously
, but was in tears and shaking with fear with no DH to cling onto as usual.
When the plane took off the woman started to try and engage DH in conversation for most of the four hour flight. He was like this
. Let's just say he wasn't his usual friendly responsive self.
So however good your case or argument or reasonable your request seems to you, you just never can presume someone will oblige.