I've never encountered this "problem" in the huge number of games I've played that had paid expansions. The whole point of an expansion is to give us something new. If you can't afford, or refuse to pay for it, you don't get it. In terms of the impact to the player, it's little different to choosing to buy a game if you want to play with friends who already own that game.
Except, if you don't choose to buy the expansion, you still get to play the game and only get blocked from certain elements of it. But, see, I've never come across this. An MMORPG releases an expansion and all my friends who wanted to play the game bought the expansion. Because we all wanted to try out the new content. When I stopped playing that MMORPG, I no longer bought new expansions.
It's so patently simple I don't really get the idea that anyone would bother to conjure up the imagined scenario where this is a problem with paid expansions. Unless they don't have any money. Or they aren't interested in the new content. The former is not FD's fault. The latter makes the whole topic redundant. It's you who doesn't want to try the new content, you are the one blocking yourself, not anything or anyone else. And why would you be bothered that you can't join your friends if you don't want to do what they're doing?
When I try to visualise this problem in a diagram, all I keep seeing is a big circular flow chart and the "problem" is off to the side in a little box, not connected at all to how things actually are in the real world.
