UPDATE: I submitted an inquiry on BMW's website after I started this thread, and a BMW Genius was assigned to my case. They spent several weeks researching my question about the overboost feature (different departments were just as confused as we were), until finally their North American specialist weighed in with this information:
- The overboost feature is real, and present in the Canadian models as described.
- The overboost feature is NOT available in U.S. models, and they don't know if it will ever be offered in the U.S. market.
- The overboost feature may exist in other markets outside of North America too, but the BMW Genius North American specialist did not have access to that information.
The BMW Genius did not seem to know if the overboost feature required hardware or software changes (or both), so I don't know if it's something we can simply (or safely) "unlock" on our US models. I also don't know if BMW beefed up the components of Canadian models for overboost (better half-shafts, transmission, etc.) to accommodate the additional power. A quick comparison of parts diagrams or phone call to a BMW tuner in both US and Canadian markets might be able to confirm or deny if there are any programming differences between X1s in these markets.
I asked if there was any possibility that the overboost information was simply inaccurate or incorrect, and they said no, it's correct and not a typographical error or mistake.