The assumption is that you'll be wearing a jacket, I think. Actually, winter shouldn't be too bad, because the sun will probably warm the inside of the cars sufficiently to be comfortable if the vents are mostly closed. When these systems are used for ski resorts, they are normally unheated, though I've heard that some resorts are experimenting with battery-operated seat warmers.
Also, FWIW, observers think that the construction of the Skyliner infrastructure may be getting ahead of schedule. Doppelmayr famously insists that its own staff do the installations, so folks who follow this industry think that perhaps they need to get it done sooner in order to move their people to other scheduled projects. All just speculation, and even if the stations and towers go up quickly, they won't be able to get it going without extensive testing (during which phase I anticipate that they will have to bite the bullet and add a/c.)
I am hoping that once the gondolas arrive, that they will park some around the property so that guests can check them out on the ground.