I can see this one happening, in a strange deal.
Something like the Cuadrado deal, 2 years loan to Juventus for 25 million euros with an obligatory option to buy for lets say 150-170 million euros.
Dybala goes to PSG on the same terms. Loan for 2 years with an obligatory option to buy.
When we buy him, Ronaldo would have 1 year left on his contract, so it would be one season where we would have an expensive Ronaldo and Neymar in the team, still an Neymar on loan would be expensive if you look at the salary. But when we buy him for a high price that would rise to another level.
Could work, after the Ronaldo signing nothing would suprise me anymore.