Is Inti-Creates still working on the game?

If I remember correctly, Inti isn't exactly not touching the core Bloodstained game, it's simply that as a development team they won't be part of it, meaning individuals within the company that don't consist of a team will still be contributors, I think the track tied with his name in the very Kickstarter itself attests to that. I'm absolutely confident you'll see his name in the credits.

Well, my comments surely don't have the same weight as Mana  's but ...

1. IIRC she's previously said they were trying to keep as many assets as possible when they switched from Inti to DICO - which makes sense.

2. DICO was hired because they had more experience with UE 4, and especially with the procedural generation of assets levels and backgrounds.

From these two facts it's possible to more or less discern the answers to your questions. DICO's likely built an entirely new game engine using UE4, so the amount of code kept from Inti ought to be very little - possibly zero, depending on who was given the copyright to the code as part of the severance deal (Don't expect to ever learn the details - these things are normally not disclosed).

As far as background assets are concerned, again, probably little to nothing, since one of the aims in switching developers was to be able to use procedural generation for the backgrounds and levels.

Since the game was only starting with mass production when the switch happened, we may infer that not much in the way of character assets was finished at that point. If they kept anything from Inti, it was the character assets whose creation they supervised, which were both finished at the time of the switch and compatible with DICO's new game engine.

In short, it was probably closer to restarting from scratch than it was to picking up where Inti left off. That said, the game's design - what ArtPlay has been working on, and Inti may be assumed to have contributed to - has probably remained largely unchanged since the beginning. So, in that sense, it's not like all of the work that had been done up to the time of the developer switch was lost.

As for the developer switch causing a delay, well, it did - that's why the game was pushed to 2018. But there's no need to worry: the wait should be well worth it in terms of the quality we're getting.

The best things come to those who wait. 

Art direction. Monster design. Environment skeleton. Some input in the caramel map and general info on what IGA can and can't within the budget. Boss patterns. Some weapon effects, speed run thoughts and ideas. The view (perspective on Miriam and level) Character basic animations. Some of the music and some ability feedbacks. Costumedesigns too. This is what is kept, translated from and based out of Inti Creates services at the moment. Some of which may have changed.

Do not wanna hype things up. But if we do the math. Time equals development, minus additional projects (like a main game) minus problemsolvning equal the prequel game minus official updates.

Since there arent any main game in focus, and no main game troubleshooting (or very less of it since they stepped aside but keep in touch with the development of the main game), would mean full time and focus, or maybe 90% of their efforts are towards making the prequel game and additional time to port the prequel game.

Inti Creates having their team on almost full force on the prequel is great news and the one thing I were thinking when this (old) news exploded.

Let me re-phrase.

The small team which were about to do the prequel-game anyways, now have an almost full force making the prequel.