You are right maybe Conte has a big plan with Lukaku, but I am not sure if relying on Lukaku alone everything will be fine. I mean if Conte really has a good plan for Napoli, he should think long term to keep getting contribution from a professional player.
Whatever plan Conte builds for Napoli with Romelu Lukaku, it should be a smaller plan than four seasons ago when they worked together in Inter Milan. 4 and 5 years ago, Lukaku was younger and a better player than now so Conte's plan around Lukaku must be different too. It is reflected by total goals scored by Lukaku in latest seasons after leaving Inter Milan years ago, even he returned to Serie A and played for Inter Milan, AS Roma, he scored less goals in a season than before.
Each player is different and not all coaches can match the style of a player like Lukaku so it is indeed clear at Chelsea that Lukaku does not fit there.
Lukaku is indeed a player who has characteristics and he has good quality but in the last few seasons his performance has decreased drastically so what Conte is doing now I think is something very dangerous and Conte's excessive trust in Lukaku could be a disaster for Conte in developing the performance of the Napoli team
Lukaku already shown that he could absorb tactical philosophy of Conte very well years ago and he will have no big problem to work with Conte again. Maybe with worse individual performances from Lukaku than before, Conte will have to adjust his plan, and use Lukaku in a different role that includes not only scoring goal task but supporting his team mates in different ways.