I think this is the most difficult franchise for them to land a win on.
If they go classic 2D or 2.5D then it won't have mass appeal sales. It would likely please fans of the franchise the most though.
If they go 3D it will be in a weird place because something like a lords of shadow wouldn't fly in this day and age.
I know there's major souls like fatigue on this board but I do think that's the best bet for a new castlevania. Think Bloodborne with castlevania monsters, and a deep interconnected world with shortcuts back to earlier areas etc. Dodge and parry system, weapons to upgrade, various builds if you're more of a whip guy or more of a chain guy etc.
The other formula that stands a chance is a 3D game for cut scenes, epic visuals etc, but all the gameplay is still 2.5D. Potential middle ground.
I would NOT suggest a symphony of the night remaster or remake. Too many diehards will rip it apart…