I’d imagine that Dorico ‘integration’ for the Cubase/Nuendo (CuBendo) world will simply use the underlying ‘engraving engine’, but keep the composition entry style (typically real time playing while recording, or using the many MIDI editors provided) pretty much like it already is in existing Cubase Editors.
The Setup Mode of Dorico, where we designate “flows, players, etc.” is already there in CuBendo. We call them ‘tracks’. And each ‘track’ can have ‘versions, and many lanes, and even independent score module layouts’. Each ‘track’ gets very powerful ‘inspectors’ where all kinds of MIDI/VST real time transformation/manipulation can take place.
The Engraving mode exists in CuBuendo, but might eventually be replaced with the Engraving mode similar or identical to the one we currently see in Dorico.
The Play mode already exists in CuBuendo. There exists the ability to work with ‘track’ instruments, or ‘rack’ based instruments, along with stacks of support for all things MIDI and VST. There are already some of the best ‘key-editors’ ever implemented in any DAW on the planet, as well as “Diamond Drum” and “event list” editors. Adding yet another Key-Editor identical to the one in Dorico shouldn’t be a problem either (but it’s currently a downgrade compared to the very robust Key-Editor already in CuBendo, which already has channel lanes for CC events, as well as ‘individual note’ containers’ that allow storing VSTexpression [In the CuBendo Key Editor, which is similar to the Dorico Play view in many respects, we can already store CC events in VST3 containers so they move with individual notes, instead of living as a lone chunk of channel data that must be moved independently of the note-on/off events]).
The Write mode is quite different between Dorico and CuBendo, so the hooks would need to be in place for CuBendo to open this UI and keep its information in a format that is compatible with the Cubase Track (I might be wrong, but I suspect this is already the case, or very close to being so).
The base audio, timing, and groove engine is already there (and probably very similar if not identical to what Dorico is using)…CuBendo already has dozens of editors for dealing with MIDI and VST data. All that’s needed is to replace the Score Engraving engine with Dorico’s once it’s mature and ready to go, and to tack on the routines that might make it possible to load a dorico score directly into CuBendo.
So, at the end of the day, all that needs to be done is to pull the engraving engine (once it’s ready) into CuBuendo, and add the ability to load/save scores in the native dorico format (convert between Cubase projects and Dorico scores on the fly).
Having the ability to open the “Write Mode” from Dorico to work on a selection of “Tracks” in the project would be gravy 
The existing CuBendo Score module already works this way. First we select some tracks, then we open the Score Editor…so…just make it so one gets the option to manipulate these tracks with Dorico’s Write mode instead. The terminology is different (CuBendo currently calls it Layouts, where Dorico calls it Flows), but it’s ultimately the same mechanics.
In the setup phase, the terminology is different, but the purpose and foundations are close enough that it shouldn’t be very difficult to convert a “Dorcio Flow” with it’s “Players and Instruments” into the “Cubendo” layout of ‘Tracks, Lanes, Versions, Layouts, and MIDI Channels (plus what ever new realms VST3 protocols add to the table)" with powerful Inspector elements and flexible routing options’.
In my mind, the only real holdup is giving the Dorico engine some time to evolve and mature; while gradually arranging the the elements necessary in both engines (I.E. Giving Cubase the ability to work with the scripting language in Dorico, and vice verse) to insure a happy marriage between the two apps.
My ‘guess/prediction’ is that someday we’ll have an option to marry Dorico and Cubase if we have both licenses on our dongle. I’m looking forward to a day when we can import a Dorico Score directly into Cubase, and I predict that day might come relatively soon. Pulling a CuBendo project into a stand alone instance of Dorico on the other hand, might present a pretty large slate of challenges that will in the least require a good bit of user intervention in terms of what extensive CuBendo data can be ‘thrown away’, or otherwise ‘interpreted’ into a written score in the conversion process.