Dorico does have one ensemble instrument: a Choir reduction.
ptram - I think you’ve worked out for yourself how to do this; via a template of Keyboard instrument definitions with manually added playback techniques and expression maps. Yes, saving reassigned Instruments as Playback Templates poses problems, but if the whole layout has been saved as a Template surely there’s no need to involve Playback Templates? Unless, of course, you want multiple different types of sketching layouts - which would seem to me to be getting away from concept of sketching and back into arranging.
Apologies if I’ve misunderstood you.