Hello,
Just to check that I am correct in thinking that, at present, there is no way for Dorico to make a piano reduction from selected instruments/staves of an orchestral score.
Thanks.
Not yet, and I think when this will be possible, you will know !
Automatically? No.
But with copy and paste in chord input mode, voice filters and all the voice tools it should be possible to create a piano reduction reasonably quickly.
EDIT: Marc was faster than I… 
Thanks Marc and fkretlow.
Yes, there is no automated way to reduce material, but I’d like to share my first-hand experience: while at first thought it may seem like more work, using Chord Input mode and Paste Into Voice like fkretlow says is a breeze. I’m finishing my first piano reduction (of a fairly big work) in Dorico, and while the materials are fairly simple (early 19th c. sacred music), I must say I’m happier like this. It seems faster than using Sibelius, where the plugins often took some fair seconds to process and you’d often have to touch or redo the result. While I’d wish to see these aids implemented in Dorico, I have to say that, as it stands, the process is pretty painless.
You are absolutely right, LSalgueiro. And this way, you still are the “master”, you know exactly what you will have on your reduction. Thanks for the tip.
WoW! Working very intensive with Dorico this is the first time I see that you can copy/paste with Chord Input enabled! That’s very nice.