Several airlines have recently announced that they will be charging more for window seats. And for aisle seats. This is in addition to the additional charge for bulkhead seats, exit row seats, seats toward the front of the plane, seats near the bathroom, seats toward the back of the plane, seats next to pretty ladies, seats next to showered people, seats more than 2 rows away from crying children, and seats which are still able to recline.
Basically all seats now cost extra except 15B. Until people start asking for 15B. Then there may be an upcharge for that seat due to high demand.
I predict that there will now be a whole lot of flights with passengers strapped uncomfortably into middle seats, while aisle and window seats remain empty. Of course, if you slip a little extra gratuity to the flight attendant …