Hi Ben - Yes, I think supporting detours from detours is probably a step too far for us in terms of complexity of the coding required! Route collections may well give you what you need though, as these can dispslay multiple independent routes on one map.
Whilst it would be nice if this issue was fixed, I think I am somewhat overusing this feature and what I'm looking for is route collections!
I would like to plot a detour on part of a route which is already a detour itself. This works, however it is easily broken: when I click on the detour of a detour without clicking on the detour, a straight line from my main route goes to the start of the detour of a detour, very frustrating. The ideal behaviour would be for when the detour of a detour is selected (and the detour itself is not selected) the detour itself would be automatically selected (if this is even possible)