In reply to Andy Patterson.

@Andy: It's not possible to open Sibelius files directly for two main reasons: most significantly, it's not practical to open either the Sibelius or Finale file formats, because to do so would require reverse-engineering a huge proportion of both applications' internal workings, which would be a massive engineering effort that would take away from developing other functionality in Dorico; and secondly, although I am not a lawyer, this kind of reverse engineering is illegal in many countries.

You will be able to open existing projects via MusicXML, which is a lot better than nothing, but it does mean that you should not expect to be able to bring finished projects into Dorico for revision – you would have some fixing up of layout and other details to do (though Dorico's default layout and engraving are sufficiently superior to its competitors that hopefully the amount of time needed to get things laid out properly will be much lower than it would be in other applications).