I kinda of wonder how much the expansions will cost and how many their'll be. I pledged up to the 2nd beta level, but I'm extremely disappointed that the physics will not at least be newtonian (one of the things that made Frontier and FFE so fun for me). So I'd like to play the game before I commit another dime to it. If they drop the ability to buy into the expansions before beta 2 odds are I won't be playing the game much past release, regardless of what I think about it, unless the expansions are few and cheap.
Also will people who don't buy the expansions be able to continue to play the game online after the expansion? Will they only be limited to playing with other people who haven't upgraded? Most games that have expansions do it in such a way they both people can still play together, but some of the things like planetary landings seems like a pretty large alteration to the game.