It looks to be one stage. I mean, one base on top of a mountain, you really can't fit three stages in, can you? But then again, you never know.
The talk of two pl maps is this:
--A long time ago, before the WAR Update, Dario told us that he was making a pl map with a twist - such as bridges that needed to be lowered before the cart could go over them, or gates to be opened, etc.
--The teaser for pl_upwards that Valve gave to a community wasn't apparently Dario's. I think zpq told us Dario said "it's not mine."
--If pl_upwards is not Dario's map, and since he's the one making the pl-with-a-twist, and since it's been in development for a lengthy time, we are assuming he is releasing it with the Engi update.
But as Nine said in the chat a bit ago, "we don't know anything, and for all we know, it might not be coming out with this update."