Official explanation from Ben:
I'll go ahead and answer that one before the concern thread: the Starfarer Gemini is significantly 'better' in several ways than the standard Starfarer (there are some tradeoffs, especially in core carrying capacity... but there are enough areas where it's different that people will immediately think it's better.) It's also a ship constructed from the ground up for this purpose rather than modified from an existing chassis. With those things in mind, it seems unfair to only allow early backers to have an LTI version. (Similarly, the folks who are most likely to buy it are the ones who have been collecting lots of ships from the start... and they'll probably also be the ones who want both rather than be forced to upgrade.)