Koji Igarashi recently did an interview with Famitsu and some new details were shared on Bloodstained Ritual of The Night.
The game is roughly 20-30% complete so far. This may not seem like much, but this could be due to being the base parts of the game, with other parts coming out faster. That said, Igarashi did note that he needs to increase the pace of development.
When it came to cancelling the Wii U version for a Switch release instead, he mentioned that the reason Switch is being favored over Wii U is that the game is being developed with Unreal Engine and ported from PC. As the Switch supports Unreal Engine 4 natively, this means that they don’t need to do any workarounds and can make a straight port. As well, the planned release in 2018 also lead to the decision of moving away from Wii U as the system is pretty much dead.
It seems IGA knows what he is doing with Bloodstained and wants to pick up the pace. I am sure the game will be amazing when it is released.