We know that there are certain games that were intented to be in their own continuities from the start such as Circle of the Moon, CV64/LoD, Order of Shadows etc., and there are also certain "retellings" of games that, according to IGA, don't take place in the main continuity either (Super Castlevania IV, Dracula XX among others). Lots of people treat Lords of Shadow like it's the first AU story in the series, but Castlevania has actually tons of little sub-continuities, each with their own versions of Dracula and the Belmonts!
I've been thinking about how interesting it would be if say, they would make another game in the same world of Circle of Moon. The world itself wasn't that special or unique, but don't really know much about that continuity, which would allow developers to come up with new, interesting story ideas, and build a new continuity from the ground up. They could give a new backstory to Dracula too, or decide to leave his origin completely mysterious. Likewise, a lot of things we take for granted in the main continuity could be omitted or altered to keep things interesting.
Of course you negative nancies would say: "Well, why bother using old continuities if you could create complete new ones, like LoS!". Well, they could still do that too of course, but sometimes putting limits on your creative freedom could lead to more interesting results. Another reason could be that, for example, if they would create games in a Castlevania IV centric continuity, they could perhaps recapture the feeling of that game's "world" in newer entries.
I'm probably really poor at explaining this, but I definitely think it would be an interesting route for the series to take.