I see. That's a weird feature. 😃 Mostly the reason I say that is it seems quite specific to one particular use case. Most of the time you want to pick the value. Having UI to define a range so a value can picked for you seems a pretty complex solution.
Easiest is to use an online random number generator to pick a number in a range, then plug it in. This does take some effort, but it's not that much. Back in the old days animators used to have to draw each entire frame by hand, 12 frames per seconds! Uphill both ways!
It might make sense to have a "wizard" that could configure physics constraints like this. Taper a value based on bone hierarchy, randomize values, etc. Since this can all be done now with a little elbow grease, it won't make it into 4.2. We must resist scope creep! The first version of a feature should be the minimum viable product, then we add to it over time, lest we'll never manage to finish things.