John Solomon's speculation doesn't impress me. I think he has a couple good sources -- but I don't think he has any close to Durham's work.
What I expect. ...
If Durham is not yet done, but he has a broad conspiracy already well established, rather than have a few minor players indicted on minor crimes -- like Klinesmith on an obstruction count -- I think
We are more likely to see a broad "narrative" laid out in the form of a lengthy "speaking indictment" that goes into great depth and detail with regard to the nature and overt acts over time of a wide-ranging conspiracy.
What exactly he opts to characterize it as a "conspiracy" to do is a very intriguing question. A "conspiracy" by definition is an agreement to commit one or more crimes. Obstructing the lawful functions of gov't is what Mueller alleged in various places.
I don't think the facts will take him much beyond that.
Then in response to this question:
Will venue almost certainly be DC (auto aquittal if so), or are there mechanisms to allow charges in different jurisdictions?
That is the beauty of a conspiracy charge -- you can have venue in any district where an act in furtherance of the conspiracy took place. My guess is that he'll try for EDVA in Alexandria.
The important thing to remember is that "an act in furtherance of the conspiracy" doesn't necessarily need to be a "standalone" crime in and of itself. It can be a facially perfectly legal act, but if it is done with intent to assist or "further" the conspiracy then it becomes a crime. Simple example, renting a car--in a different judicial district--with the knowledge that it will be used as a getaway car by others who may stage a "theft" of the car. Venue for the overall conspiracy could be in either district.