How strictly do you want to define "minivan"? The Tesla Model X is plenty spacious, with 37 ft³ behind the rear seats or 85 ft³ if you fold down the rear seats, or you can fit in a 3rd row of seats (which reduces the space to 15 ft³). The doors go up instead of sideways, but as long as it can move all of your stuff from A to B, does it really matter which way the doors go?
It’s hazy. It depends on your need to seat either adults or small children in the third row. The X is in the size class of SUV where regular third row use is viable, but it’s still harder to work with car seats or to climb back there. A minivan’s being boxier allows a full width third row and easier access through the middle row.
Compromises in loading and unloading passengers become tiring with an SUV if your main use is city/highway transportation and you have 5+ family members. Older elementary is the only age where SUVs work fine since they don’t need any help but are small enough to easily squeeze back there (plus they think it’s fun.)
Large SUVs make fewer seating comfort/utility tradeoffs but they’re a lot more expensive than vans, so perhaps economical seating is part of the distinction. The Sienna and Pacifica are the nicest van hybrids and are around $30k less than the X.
Yes, car seats are the biggest deal if you have multiple kids in car seats (of course most people don't, so they don't think about this). We have an Odyssey because it was (is?) the only minivan with latches and a tether in all six locations, and the middle seats can be removed or slide back and forth, giving us maximum flexibility for arranging our four kids.
It's nowhere near as spacious as an Odyssey or Sienna or Caravan. Nor as nice inside, IMO. In fact, the model S actually has more usable cargo room than the X. The X is just a tall car with a sloping roof that kills all the usable space, just like all the other crossovers on the market. If you want space, you get a van. If you want a tall car that just has a high center of gravity for no reason, then you get a crossover.
Have you never seen young kids open conventional doors right into the side of an adjacent parked car? That's one of the big advantages of a minivan vs. SUV. But it does look like the upwards opening doors would solve the same problem. I'm slightly concerned that my kids would try to hang on them as they go up (I've seen it done with our garage door).
