In the bad old days, before Sibelius existed, I often used to write a passage with instructions such as sempre staccato or sempre marcato underneath. I didn’t have to cancel this instruction because to a human it was obvious when the instruction was no longer valid.

When Sibelius came along I simply used accents and staccatos on all the relevant notes to avoid confusion and to get correct playback.

How will Dorico treat such instructions and how careful will one have to be to mark the ending of them? Or will it still be best to be precise about every note?

On a related topic, will the often found articulation tenuto staccato be available as an indivisible unit?

That depends. If you can describe an absolutely unambiguous set of rules for the point at which the instruction is no longer valid then I’d say ‘probably yes’. However, coming up with an unambiguous set of rules for anything that does the right thing 99% of the time - that’s the hard bit…

(actually, not strictly true, the hard bit is turning that into C++…)