You mislabeled your graph.
"Bitcoin XT adoption" should be labeled "Bitcoin XT + NotXT + Pseudonode adoption."
Good luck observing RealXT's actual adoption with so many FakeXT nodes feeding you misinformation.
Also, the total FakeXT+RealXT adoption curve has flattened over the last week, as the public became better informed about XT's Tor Blacklist, IP reporting, potential catastrophic consensus failure, and Mike's "Final Call."
Core 0.11.0 has flattened moar and before. Perhaps because they are implementing customized core + BIP101.