it can be as complex or as simple but in the end question would be what is implementable. in scope of RW the simple the better. and somewhere along the line it is going to cause annoyance in either of cases (usually happens with parents with many children spread all over

another simplistic approach could be to have more layer icons (like we currently have) but labeled different like VSM(virtual sub mix) and all the layers having same vsm icon share same settings and if icon is changed layer becomes independent. (it could be a bit limited though, but perhaps 4 icons for bass, 8 for gtr, 4-6 for keys, 4-6 drums and perc, and perhaps few more for others ).
of course when duplicated it will have the same icons so automatically will be part of the same group.
at the basic level, it can be any duplicated riff/layers shares same set of settings, unless explicitly made independent.
Or
you could have a submix view where you could assign a layer to one of the submix channels and let them control your layer and fx or your layer could go directly to master. but this would again be a bit complex.
btw, i am thinking more of a sibling kind of relation between layers than a parent/child. where change to one sibling reflects onto the others, in case of parent/child if a parent layer gets deleted/deceased then all children get no clue where to inherit from.
plus you always need to keep track of who's the parent, to go in and change the settings. if you decide later on to add something to the parent riff, and across some of the children later on, the direct inheritance might not work.
In case of sibling , you just need to tell one that you share same settings with that of like kind and it inherits from another. (it's similar to parent/child,but here the active layer becomes the parent for the group when you turn a knob/dial). offers a bit more flexibility as it can allow you to control not just a duplicated part but even a different lick/phrase/rhythm layer in another riff having the same settings (same guitar patch and fx) as it becomes a somewhat virtual track.
btw guys don't get me wrong, i ain't dissecting or blasting any of the ideas given (never ever has been my intent), they all are great and will be more than happy if any one of these could be implemented).
i am just thinking out loud and sharing/discussing ideas with you guys.
now i seriously need a beer at breakfast time.

I Am A Man of Few Words Ironically Understandable by the Select Few, hence more often than not I have to Come out of my Manhood to do the obvious. Now Ain't it a cruel world?