The two games I'd love a remake of are Legends and Simons Quest. I love them both (despite agrivating flaws in legends), but here's why they both deserve a remake:
Legends:
Fan ficy plot, taken out of cannon as it doesn't fit with the plot of CV3. Update it to fit into Iga's timeline, refine the gameplay a bit, make better enemy placement and fix up the level design. Plus, the plot is barely there in the game, meaning you'd have to read about the game elsewhere to find out why Sonia is after Drac and her relationship with Alucard (which would most likely have to change, unless it is set after CV3 as a gaiden). It could make for a great story driven action game, prefer revolt still in 2D. Plus, they need to update the useable of the souls weapons to make them more appropriate to more situations, cause it's one of the feature I love in Legends and it wasn't implemented too well. Also, make Burning mode its own separate button lol
CV2:
I love CV2, but imagine a huge 3D open world with that horror setting? If it stuck true to the source, it'd be extremely unique and amazing! Like you mentioned, make it like the Witcher. So much potential there. Plus, we never got Sinon in a 3D game (Judgement doesn't count cus of how TERRIBLEY they neutered him)