Surprised no one mentioned this. No one seems to be discussing it as well. This means not only will you not be able to build from low ground to high ground, You also can't warp in from low ground to high ground.
I feel this is a terrible change. We've already gotten the pylon radius change, vision up ramp change, and warpgate change to stop 4 gate. I feel like it removes a few tactics that the protoss can do. For example, I remember watching a GSL game on Xel'Naga Caverns where a pylon was placed on the low ground near the opponents main, and using a hallucination, gave vision to warp into the high ground to attack the main base. With this change, that tactic would no longer be usable by the Protoss.
I feel like the Protoss are being unfairly punished for a PvP issue in PvT and PvZ.
This also stops some creative placement and simcitying such as placing a pylon the low ground, and then placing gateways on the high ground to make it difficult to unpower.
A very very recent game I played today in fact, would unfairly be affected by this. I was cross positions on Antiga Shipyard, and I took the bottom gold. I put pylons on the low ground right near the gold mineral patches. Then I placed cannons up onto the high ground to help cover the watchtower.
Another non cheese, non gimmick example I thought of: When you're going blink stalkers and you blink into the main, you can reinforce your blink stalkers by having a nearby pylon with power radius onto the high ground. Now you can't do that without having to use up a blink. You also cant use zealots of sentries for warp in reinforcements.
P.S. This change still won't stop PvP on Taldarim from being 4 gate vs 4 gate.
P.P.S I also think people need to realize this hurts Protoss harass way more than Protoss cheese. Cheese is reliant on lack of scouting, if you don't scout well, you're still going to get cheesed. Regardless of this change or not.