If I had a Sig X reservation, I'd be canceling now. Folding rear-seats are a must-have for me, too.
I completely understand that many people don't care about folding seats; and like OP I am honestly happy for them. And I can see some reasons why Tesla may have gone with one configuration before another to get the car out; I'm not upset with Tesla for offering non-folding seats, at least at first. (On the other hand, after being told they were coming, putting down serious money and then waiting for a few years, I don't think it's hard to see why some are a little disappointed and it hurts to cancel).
Not that it really matters, but as an aside: What I don't understand is people that sound shocked that some of us really do haul stuff in our cars. Even expensive cars. The price of the car doesn't matter, it's still the car I'm driving, and if I have to haul something I'm going to use it. It's a rare week where I don't fold down the rear seat of our Model S - which happens to be able to haul much longer stuff than the X can. (Yeah, yeah, it depends on the shape of the cargo, how many passengers you have, etc). I carry stuff a lot more than I carry passengers. I don't have any problem believing that some people don't carry a lot of cargo; why do some have trouble believing that others do? It seems odd, but is of no real consequence.
Fortunately I don't have a Sig reservation, so I'm going to hold on to mine; and likely defer when it comes up. Maybe that will give me as long as a year to wait and see what happens. Maybe Tesla will offer a folding seat (they likely wouldn't say now if they were working on it, as they don't want everybody to hold off and wait for it). Maybe my needs will change - for example, if our parents get to where they have to sell their cars, having a vehicle with really easy access for passengers with mobility issues may suddenly become a priority. We shall see.
(I already have two Teslas, so it might be easier for me to remain serene as I wait for something that fits my needs better).