It only makes sense if Chelsea can win - otherwise Osimhen will only ruin his career, especially if he stays there for long. If he needs to win, it's a mistake to move to Chelsea. He needs to choose another club that can most likely at least win their league and who are decent in the Champions League. It's hard to say exactly which club would suit him and even more so which club would be able to accommodate him, but definitely not Chelsea
Osimhen as said by their president in Dicember is already sold but we dont know to whom.
A reason on why we dont know yet is because it may go to EUA and there the market session will start in 1 week.
It may also ends at PSG, they needs to replace Mbappè somehow even if they are not spending so much money lately.
So TLDR, Napoli will have the money from Osimhen and they can spend for Lukaku.
If you look at the current situation with rumors circulating, it is certain that there are only 2 possibilities where Chelsea and PSG are strong candidates. Although we will not know what will happen in the future but by looking at the money power of these two clubs as well as rumors that do discuss Osimhen's move, it is undeniable that it is likely that these 2 clubs are the next destination especially Napoli must want a high price for its star which is certainly difficult for other clubs to give.
However, there could also be another surprise where there is a new club that can bring Osimhen without us knowing because the rumors are covered just like the case of Gakpo who went to Liverpool last season even though the rumors circulating at that time were Manchester United.
What is clear is that this will not be open for long because after the euro is over summer transfers will get busier and that's where we might get answers to Osimhen's future.