It isn’t as simple as creating playing techniques, because multiple staves would have to be affected. Specifically, along with a sample change on one staff, one or more additional staves would need to be silenced. There is no provision in Dorico for altering playback on a staff from some other staff.
Because I want the consolidation and splitting of staves to be automated entirely. If I write for multiple instruments on a single staff, than I am manually condensing notation. I want Dorico to do that for me.
For example, say I have three trumpets playing the same notes. In the full score, they condense down to a single staff, with “a3” notation applied to them automatically. Later, I decide I want one of the trumpets to do something different for a few bars; all I have to do is alter the notation on the one staff, and I’m done. I don’t have to manage multiple voices on a single staff, I don’t have to notate how many instruments are playing (“a3” or “1.” or “2. & 3.” etc. – Dorico handles all of that), I obviate the messy scenario of solo staves and a unison staff, I’m not required to split and rejoin the staff manually when the notation gets crazy, etc.
Ideally, I wouldn’t even have to bother with manual voice changes, but because Dorico isn’t smart enough to work out the playback, I’d still have to set one or two of the staves to different voices (one at solo, and one at a2 if that sample is available). That would take minimal effort, though.