If I had to guess, this will be the final season... the fallout with the writer being a big reason, but its hard to say since the show seems to be very successful in terms of viewership. If the show continues to a 5th season, I'm in agreement that the show needs a reset with a new Belmont, in a new era. I would vote Simon, but with how much Alucard takes the spotlight, I would guess they would jump straight to Rondo and SotN.
It's been an interesting and bumpy ride so far, and my enthusiasm has declined with each season, but I'll tune in for season 4. My main concern is that each season has felt less like Castlevania than the one before, and there wasn't much at the end of season 3 to entice me as a Castlevania fan to look forward to more. If anything I'll tune in to appreciate the art and animation, one aspect of the show that I think has remained strong throughout.