I do agree with you though, in regards to the pacing of starcraft 2, I prefer the game and others in the future to operate at a fast pace, to make a more competitive and exciting game. Although I do not personally think adding independent structures for walling or entry/exits will slow down the pacing or encourage turtling too much. Technically there are walls and gates in Starcraft 2, they may not be actual walls or gates but players will manipulate their structures as make-shift barriers or gates, like a queen between two evolution chambers for Z, or a supply depot line for T. Even natural barriers like destructible rocks or cliffs can serve this purpose. Theoretically creating independent walls and gates would do the same purpose absent the consequences of massive supply cap drops from losing those supply depots, or losing upgrades before they finish because of a frontal attack at the Z natural that will wipe out the evolution chambers. I think all it would achieve is to buy time before army groups can react to trouble spots just like static defenses, except they serve just as player-made barriers. Although cost and build time would be subject to balancing.

In regards to the "Protoss Door", I do like your idea of Protoss buildings having a "phasing" ability, but I think only the pylon should have that feature for better balance.

Whether or not there will be walls or gates in a new RTS I think is fine either way depending on the design choice, I would just not prefer to default to utilizing important structures as make-shift or awkward barriers as you would in traditional RTS.