Mirror Modifier: “Left” & “Right” vertex groups

I think the feature of Mirrorring per Vertex is fundamental, but I used to imagine a different approach (that could be more suited for the current state of Vertex Groups Panel management of Blender, which is a bit limited: no hierarchy to organize different 'types' of Vertex Groups, so in a Rigged Model Mesh Object employing Mirror & Armature Modifiers, there would be a giga-list of Vertex Groups --very hard to navigate). Well, in the case our Devfellows develop hiearchy 'folder' system for Vertex Groups Panel, then your approach might be fine (especially if the system Auto recognized the Mirror Modifier Vertex Groups and placed everything in a Mirror Modifier 'folder' already).

My concept, on top of the Mirror Modifier having the proposed Optional, Target Vertex Group, is that only the 'Original' Side of the Mesh (i.e., the 'Non-Mirrorred' Side) will take Weights for that special Target Vertex Group, and then whichever Vertex that contains Weight value higher than 0.000 (e.g., 0.001, 0,327, 1,000), would already trigger the 'Enabled' Option (i.e., a Target Vertex Group was Assigned), will get the Mirrorring Modification, and whichever Vertex Weighting exactly 0.000 or just not being present in that Vertex Group Selection (Zero-Weights, Black Color), will NOT be Mirrorred. I think it would be cooler, of course, if there was a kind of Vertex Group Weight-Paint type which were Boolean (binary, 0 or 1), instead of a Gradation; that would be perfect for this kind of Vertex Group Target for Mirrorring (which I believe can't help but being a Boolean thing; well, I don't see atm how it could be useful having 'Gradual Mirrorring' anyways😸, but I think this is for the Designers to address).