Even though Jordan did started writing the incest storyline with some well-written romantic overtones in season 1, but I agree with you that Cesare & Lucrezia's incestuous relationship may have far exceeded Jordan's initial intentions. If we consider his statements from saying that he wanted to portray Cesare & Lu as the perfect couple if they weren't siblings during S1, to arguing that there lacked any real evidence to prove that the siblings actually had an incestuous relationship in real-life while filming S3. It does imply to me that Jordan may have initially just wanted the siblings' relationship to remain strictly emotionally incestuous, I don't think he initially intended for Cesare & Lu's relationship to evolve into a physically incestuous one too. I think the fact that Cesare & Lu's forbidden love became much more passionate and intense both emotionally and physically in S3 was the result of the incredible chemistry between Francois & Holly, strong influences from other people (particularly from Francois & Holly) and the huge popularity of the Cesare & Lu incest plotline
