I agree re Messi not coming to Inter. He loves Barca, I don't see him leaving at all despite the rifts this season. I think he will remain at Barca even post his playing career. Its his legacy he will be worried about now.
But just for a moment lets assume the hypothesis that Messi wants to come to Inter. In such a scenario, I can see Suning going for him. They have bought Inter for profile, almost like a global PR vehicle. And there is no signing like Messi when it comes to that. Imagine what something like this would do to their business in China and elsewhere. And as far as finances are concerned, Messi may cost 50m+ in wages per year, but he will fetch at least half that in revenue increases from sponsorships, etc. So financially I don't see a move like this out of Sunings reach or ambition.
The only question will be of FFP. But with the recent legal victory of City over UEFA, FFP is on life support. You can be sure that a few big clubs are now going to take on FFP in the next year or two.