Oda said he wanted to end one piece in 3 years. I don't see how or why he should fight both.
Zoro already surpassed the YC1s when he defeated King. Why should his fight in the blackbeard pirates be against an opponent on a similar tier?
If you've noticed, there's a clear jump in tiers in the opponents zoro(or any SH) faces.
King>>Pica>>Hyouzou
I don't see how Oda could hype Shiryu to be that much stronger than King, unless Oda goes the Shiryu kills mihawk route.
Assuming Oda didn't lie about the series' timeframe, which tbh makes sense as Luffy has almost found one piece, either Shiryu>Mihawk or teach allies with cross guild. I'm guessing its going to be the latter.
My EoS matchups:
Luffy vs Teach
Zoro vs Mihawk
Sanji vs Aokiji
Jinbe vs Crocodile
remaining SHs+grand fleet vs Blackbeard pirates