With bigger batteries, the need for faster charging *decreases*.
I've already installed a 16A 230V (3.6 kW) socket in my garage for the Model X, because I really don't need more than that. The battery easily covers a week worth of driving, and if I return from a long trip with an empty battery, 8 hours of charging replenishes more than enough range for the following day.
On the other hand, if I had a Leaf or something similar, I would find myself in situations where I would return home from a trip in the middle of the day with close to zero range, and then need 100 km a couple of hours later in the evening. Then I'd need ~10 kW charging, so that I could make that evening trip. (Without using a rapid charger.) The Model X covers that use case with no additional charging.
I think the rumor could be accurate, though. I've been suspecting the charger could be getting an upgrade, after the dual charger stopped being available in the design studio. It's apparent the dual charger isn't something Tesla wants to sell, so they are likely to replace it with something better.