It would be funny to see a stretch goal for something that was already completed; I don't think it would encourage many extra backers or tier upgrades. Mac and Linux were not stretch goals in the D:OS kickstarter; porting resumed when the initial goal was met.
I don't know. Are you hoping to get a refund before the imminent news about the Linux version is announced?
Larian is focused on updating the game, and there were multiple conformations that the Linux version was still being worked on, and several updates. One could certainly argue an earlier update about the delay would have been better, but at some point diverting resources from what you are working on to provide updates, that are ultimately not going to make a difference, is counter productive.