Interflug, a charge for pre-assigned seats together has existed for many years now.

Before I used to work at Heathrow, where I have been for the last 3 years, I used to work at Gatwick for a different ground handling company, and we represented a number of the major charter carriers, First Choice being one of them (they are obviously now part of Thomson!), and back then they used to charge £5 per passenger to pre-allocate seats together…of course this was/still is a nice little earner for the airline/s, because they still retain the right to move you from the seat that is pre-allocated to you (a pre-allocated seat is only a “request”, not a gaurentee, according to them!). We used to have lots of complaints from customers who had paid for this service, and were then either moved or not assigned seats together, and the airlines were unable to offer a refund at the airport, so customers were instead made to go via Customer Services (dialing an 0870 number, naturally!), and taking the cost and hassle of doing this into consideration, many people thought it was not worth it to try to claim it back.

On the flip side, Continental have a rather good system in place, which allows people to reserve premium seats online in advance or at the airport for a fee, and if for whatever reason the person is unable to sit in those seats and is moved into a standard seat, the money is then automatically refunded back to the card that the money was taken off of.