I have to be sincere, I never saw this definition involving marketability anywhere, this is new for me. Perhaps it's really like you say, but that's not the definition I had, nor the one I see as the generally accepted one when checking up the definition of capitalism.
> For a version of your example, if everyone owned a fixed
But that is the thing, it isn't fixed. You are free to manage it, sell it, buy it, as you wish. That's why it's an hypothetical situation, where everyone would end up with a part voluntarily and not forced by the state.