It sounds so obvious that I'm surprised it's not yet implemented. Currently, you can select several instruments into the instrument box and remove all, but not drag them together. Maybe it's a topic of optimization. If you have many selected instruments, and many written patterns, Renoise will modify many hit values. But you could set a limit, say 10 instruments?
To me what I would like is that the instrument box would allow grouping in groups the instruments (include name of group) and the use of colors associated with tracks or groups (manually or by routing). That is, a clear method for classifying instruments for medium or large projects.
Development of my tool: GT16-Colors
My API wishlist R3.1 (updated 24 July 2017):
My Renoise 3.1 wishlist (updated 18 July 2017):