As always, you are getting things the wrong way, first, it wasn't the directors decision for what platform the games will come out, but the companiy's.
last i checked, IGA worked for Konami. He IS part of the company. But it WAS his decision to constantly reuse sprites and game assets wherever possible that decreased the quality of games past Symphony of the Night, with some exceptions. Especially later entries like PoR and DoS which effectively almost killed the franchise, and Castlevania Judgement, which drove the nail into the coffin.
So don't complain about low quality, when it was the company's fault.
Let's put it this way. If they gave free reign to IGa again. What do you think he would do? He would blow whatever budget they give him, and he would never be able to deliver on the same scale as LoS. So his budget would be lowered again, and his bad practices would resurface. One of the many problems was not just asset reuse, that was the least of anyone's worries- The biggest problems were gimmick driven gameplay. He always designs the gameplay gimmick first, and THEN he builds the game around that and tries to force the story to fit it. It works alright when he makes original stories, but once he starts making 'sequels' to other games in the timeline, he finds a way to screw it up bad.
DoS is just terribly written and terribly presented, and started a horrible trend where IGA tried to appeal to younger audiences.
PoR was nothing like Bloodlines, and is a disgrace of a sequel, and suffers the worse case of asset reuse in the entire series.
LoI had an interesting premise, but was plagued by dungeon crawler syndrome, with flat uninteresting maps, and somewhat stiff controls. Not to mention sub-par graphics for the time period it came out. And then the small story problems that arise, such as Mathias being totally absent from the entire game, only to show up at the end and reveal his betrayal, and somehow expect us to really feel anything other than "Oh. Ok. so that's where Dracula came from".
And CoD- Well, it took the tolerable problems that LoI had with it's level design, and multiplied it tenfold, making BIGGER, FLATTER levels. And introducing a rather stupid plot, that only furthers the "anyone can defeat Dracula" problem that has ever plagued the series. (I dont care if the game says "he was bestowed with a fraction of Dracula's power so that's why!" No. it's bullshit.)
Do I even need to start on Judgement?
IGA's judgement was failing, and by the time he made another GOOD game, OoE, and then CV the Adventure Rebirth, it was too little too late, he had already doomed himself.
Second don't forget that the series started as 2D
So did every other videogame franchise from the 80's and 90's that now enjoys frequent 3D games. (except Mega Man)
And they began their attempt for 3D, when 3D became a trend.
It was not just a "trend" it was a breakthrough in technology, that actually allowed a third dimension, WITH good quality. Look at some older 3D systems, they could not hold a candle to what the N64 and PS1 (and even the Dreamcast) All because they started 2D and went 3D when it went big, means nothing. The series evolved and grew. it's natural.
Third, there was the 2D Castlevania games and the 3D Castlevania games, i can't see why they can't continue to exist together?
They can. Just don't let IGA near them, or keep him on a very short leash. At least make sure to keep his very bad development habits in check.
Without past, you have no future and those who have forgotten their past, are doom to live it again.
We are talking about a "storyline" here. nothing else. if the classic continuity must be sacrificed for the series to be reborn again and refreshed for the modern day, then so be it. As it is there is just too much baggage. the only people who bought the games IGA released were the fans, and his attempts to bring in new ones failed. It's a similar problem with Mega Man. There are too many series and too many protagonists to be able to successfully "relaunch" it.
Also if you were getting the time to read the new interview with Yamane, you would have read that what Konami does now with the series is some experimenting and also learn some other interesting things.
And LoS is one of those experiments, and it has done tremendously well, and while Cox and MS will make no more CV games after LoS2, I do hope that the bar of quality that LoS has set, is not lowered back down to the low standards we previously had.