As it is, “hide empty staves” is in a fairly good place (as of 3.5 at least) given the presence of Manual Staff Visibility: once all the music is complete, cast off in its final form and so on, you can then choose whether to activate Hide Empty Staves (after first system) as a universal default and then manage exceptions with Manual Staff Visibility, or vice versa. This covers all possible use cases, although it’s time-consuming and a bit of a pain with very large scores.
However, the typical Hide Empty Staves-like behaviour as used by music publishers in orchestral music, and therefore a default I would have assumed Dorico wanted to emulate, was that empty staves are hidden when a significant number of instruments are silent—and, specifically, when it’s possible to fit more than one system on a page. In fact the second one more than the first seems to be the overall “rule” under which hiding empty staves usually takes place: if only one system can fit on the page (in orchestral music or other large ensembles where one page = one system), empty staves aren’t hidden; if you can hide enough empty staves to fit two or more, empty staves are hidden. This rule obviously may not always work with Dorico (I’ve noticed that at the moment Dorico kind of ignores shift-X and alt-shift-X text when calculating staff spacing, occasionally leading to overlapping systems) but it being a rule might make it possible to program in as an additional default, even if it would be processor-consuming by virtue of having to recalculate the staff-hiding behaviour every time the casting-off changes. (But then that happens anyway as things are.)
Suggestion is not a very significant one, since we can do this manually once a score is substantially complete and its page layout finalised, but potentially something to look into if this feature ever needs to be revisited?
Also if this default already exists somewhere that I didn’t see, just ignore me because I’m clearly a dumbass.