At least on the old cars, wheels on BART are not cones. I keep wondering how much money running custom trains on a custom gauge costs them.
[1]: https://news.ycombinator.com/item?id=28350423
[2]: https://news.ycombinator.com/item?id=28350667
The problem with this is that newer technologies were not competing with rail purely on the technological merits, but with rail's massive amount of competition in suppliers and economies of scale. It turns out that with not a lot of effort, you can apply much the same savings and technological improvements to traditional rail, except without the huge added expense of converting to a standard you are currently incompatible with. Newer technologies have the reverse problem, in that they have very few, sometimes even a single supplier, and are basically custom projects with all the expense that entails. So the monorails, PRT, maglev, and other weird system are mostly unique specimens, or very few in number.
I've yet to see a photo of a BART wheel up close, nor an explanation as to why they supposedly chose a cylindrical wheel. I've looked. I can't imagine the design decision happened without some knowledge of why conical wheels were used in the past. Call me skeptical.