Would be lovely if it could be saved in template song.
You can save your current layout underneath one of the eight the upper right preset buttons.
I could be wrong but isn’t the preset 1 layout presented by default?
Try saving your instrument settings up front underneath preset button 1 and then restart Renoise.
Ofcourse, the layout probably won’t change if you create a new song if that is what you want, but in that case you can still always hit the F1 key.
Great idea, unfortunately it doesn’t show preset 1 by default, but that would be neat