I would be disappointed if it would be exactly like the DS and GBA games again. Now would be the perfect time to think of a new gameplay system. Personally, I hope they retain the RPG elements. Assuming, of course, this is actually going to happen.
This is one of the reasons I adore Aria/Dawn of Sorrow so much as a game. It's one of the Metroidvania's I not only replay on a regular basis, bit that I actively try to do/collect everything in. It's just that fun and feels different from the other titles.
I'm on Aria now on my play through and your thoughts ran through my mind. I hope they don't just depend on the name and nostalgia to sell the game if it is a direct sequel.
While i would like to see another Castlevania game, i would prefer to be for a home console and not a handheld console, specialy if it's like the rumor of the sequel to SotN. Also i can't stop but feel, like this is a way from Konami to mock Iga if this is real.
Konami: So you thought that you will quit from us and go and do your own Castlevania like 2D games? Take that IgaCastlevania Symphony of the Night 2
Iga: What?
Konami: So now what, are you gonna cry, beacause we have stealed your little baby?
Iga: Ah...sarcasm. 'For what profit is it to a company if it gains some people, and loses its respect towards its fans'?
If the game is real, this isn't far fetched. They may have noticed there is still interest from fans in Metroidvania, who knows, maybe they sold better in Japan (I know Dawn did gangbusters over there at least), and decided to go back that route.
If they've been working on it for a while though ( enough that a demo is ready to play on the showroom floor) however, I think it was more or less they just didn't want IGA on the project and either flat out lied to him about the game, he's under contract and has to lie about knowledge of the game but left because he couldn't work on it.