Yes, UVU. And also yes. If I find myself needing something low-level and performant, I have a hard time justifying the ramp-up time required to use D since there is a near zero chance I would use it in my current or future employment. While that isn't always how I decide what technologies to use in my personal time, it definitely is a factor that tips the scales towards a more mainstream language
It is not a border, ofc. It is just a "mental concept"; and not a hard cut. There are villages/cities where both languages are spoken/understood. So one language spoken gradually changes into the other one.
The answer also includes a link that shows many other representations including Einstein's "4d generally covariant tensor calculus".
The point is that the most common formulation today is not the one Maxwell made (with 12 equations). The idea is preserved, but it was Gibbs and Heaviside that formulated the current 4 equation representation.
