I think the sequel ought to focus on what connects the ending of LoS to the sting (ie, how we get from "Gabriel defeats Satan" to "Gabriel is Dracula"), assuming they don't do that in the DLC. Currently, we don't really know anything about the Belmonts (we only know of one of them, even), or what happened in Romania-in-Scotland during the intervening time. I'd rather they worked on fleshing out the middle of the story than jumping straight to the end from the prologue.
So yeah, a Belmont for the sequel, preferrably telling us how everything went down and maybe working on giving Castlevania itself some backstory; after all, the series is named after the castle, but none of the origin stories have ever really gone into what the deal with it is, who built it and why, or what the demon it's formed from thinks of all this.