i like to explain you another idea i am thinking of a lot.
If there would ba a second layer (in analogy to layers in Photoshop) of the pattern you could crossfade in it (or back to layer 1) with a fader on the master track and record it to an effect lane.
This would be a great new feature for breaks and mix things up much much easier. Ofc i know it is hard to imagine how to realise it but maybe someone here has the right idea to make it possible.
I am already working with groups, it is not the same and much more complex than using an overlay pattern.
It is again a question of the workflow. Your idea is a lot of work, overlay pattern is easy and fast plus you have a better overview if you work with only one screen. It would give Renoise a new dimension and new possibilities.