yeah, the ssd is removable and can be swap out for a larger capacity version. but this is an apple exclusive design for their laptop, which is very proprietary. so by next year model revision they will probably change the dimension of the contact socket a little bit to accommodate for any higher bandwidth controller. so even if next generation ssd drives were to be larger capacity and cheaper in cost, it will probably not fit in the previous generation model.
an owc ssd drives for the mac is still very expensive compared to regular 2.5" ssd drive of equivalent capacity. plus they uses a sandforce flash controller which is known to have flaky reliability.
and it makes me wonder, like when you upgrade from a 256gb ssd to a 512gb ssd which cost another $500 for the upgrade, you dont get to keep the 256gb drive, even though you pay another $500.
well then why don't you just buy the 256gb model, and then buy another 512gb extra drive as a spare parts, and you have two drives for the same cost, or just sell the smaller drive to recover some money.
or am i missing something here.