I've been a somewhat vocal critic of the U.S. implementation of Rex, and I personally experiences the "limp of shame" (speed reduced to 25 MPH) up a mountain grade in the first couple days of ownership.
I plan on doing the "coding" for maximum control (I have the cable and software-- just need a block of time), but, depending on how BMW does the announced changes, I think the forthcoming software tweaks could address essentially all of my concerns. Conditioning yourself to ALWAYS use GPS for longer trips is a bit of a hassle, but not big deal.
Here's how they should do it:
Primary objective is to intelligently use available fuel (gas and EV) to maintain full speed/performance for entire route. In other words: ICE-equivalent performance consistency.
Secondary objective is to provide as much advanced warning as possible if the Primary objective is impossible.
The car knows your typical driving patterns and it knows your intended route (including elevation changes). The obvious basic function is to switch to a hold mode at higher than 6.5% SOC in advance of a big hill ("smart hold"). But it needs to be smarter than that. It should also take into account your driving habits. If you typically drive 15% above posted limit, it should use the "learned" value instead of posted limit in its calculations. Finally, over and above "smart hold," it should, if needed, run the REx at full load to ADD charge in advance of the hills. Frankly, even in a flat road situation, if I am driving 80MPH on cruise control, it should run the REx at full load well before 6.5% SOC so I can cruise at 80MPH until I simultaneously run out of gas and EV (in concept only-- you'd hope to find gas and/or charging before then).
As noted above, if ICE-equivalent consistency is impossible, it should warn you ASAP. Note that in some cases, it will know this before you even start your journey (e.g., you are at 15% SOC at the base of a hill you are about to climb). Car should then say "insufficient charge for full performance on your journey, charge before departure or drive moderately to avoid significant loss of power." (or whatever)
