So, I've been living in Molden Heath since April. Planetary Conquest was released over the course of May.
Pre-Conquest the region consisted of my ~50 pilot corp, a ~30 pilot corp, 2 ~15 pilot corps, and a several much smaller groups. There were two alliances living in the region but splitting their residence between high-sec, low-sec and null-sec, one an 84 pilot alliance, and another 196 pilot alliance.
Leading up to the release we immediately had the 121 pilot alliance NMG. move in to support their DUST section. They were blue with the 2905-strong Rise of Legion, who were actually more like 2300 DUST mercs and ~600 pilots. They moved into a system together and started knocking over POCOs and POS 3 jumps in every direction.
By release date, two faction war space refugees arrived and blued up to take over EUtz dominance, -DARK with 250 pilots, and WEAZL with ~30.
Shortly after release EoN. appeared with 76 pilots and ~1100 DUST mercs. TLML, a very old 36 pilot corp started roaming the area again recently after a long period either out of the region or inactive.
Now all of these numbers are on-paper pilot counts, and you can assume an average of 2 pilots per player and 2 players per low-sec in-space pilot, so in summary the USTZ picked up ~150 pilots in space and the EUtz picked up ~70 pilots in space, which is has had quite the impact on a region of 28 low-sec systems, and a starting value of ~100 in-space pilots.
TL;DR Using my very rough estimations and experience living in Molden Heath, Planetary Conquest successfully took a 28-system low-sec region from ~100 pilots to ~320 pilots.