I suggested that (for Schewe?), and got the impression that certain underlying implementation aspects made this unlikely.
I do agree that for the user, they are just different geometrical approaches to defining a parameter-controlling mask, and it makes no apparent sense to distinguish between them. We just want to define some area (with soft or hard limits) where e.g. exposure is up +0.3 Ev. If Lightroom continue adding Gradient, Brush, Radial, Rectangular, Triangular, Line etc tools it will become silly at one point.
Painting in the red overlay using any combination of brush, "GND", radial/rectangular/... helper functions seems like the most user-friendly approach. I am not sure how after-the fact re-editing (adjusting the graduated width or angle of the Gradient) would be presented in a unified manner, though. Just producing a static red blob might not be ideal.
This depends on how you think about factoring the controls.
Currently the controls are factored first by tool type (brush, gradient, radial filter), then by the type of adjustment (exposure, contrast, saturation, etc.). So essentially you pick a tool to make/change a mask, and then you decide which subsets of adjustments to apply.
Another way we could have factored the controls is by type of adjustment first, and then by tool type. For example, you want to lighten an area by 1/2 a stop; then you use any of the available tools to help you define that area.
Both approaches have their advantages (Ps has both), but currently ACR/Lr implements just the former.