Wow, that's truly tempting. I think Messi might find it hard to refuse such a tempting offer, especially since Inter Miami seems to be making no progress. The club has players who aren't on par with Messi, and Inter Miami seems weak. Moving to the SPL would be a new and certainly more exciting experience.
If both superstars were in the same league, it would attract a lot of attention. The SPL's shortcut to making the league globally noticed is by utilizing its resources to acquire star players who are difficult for other developing leagues to follow.
Cristiano Ronaldo, Neymar and Benzema did not make big changes for Saudi Professional League and Messi will not have any magic to make it happens for them. Saudi Professional League can continue their super star and star player purchasing strategy but it's very short sighted. In long term, they must focus on their academies, nurture youth players who are future of Saudi Professional League and Saudi Arabia national team.
Messi has more traffics on social media than Neymar and Benzema but he will be like Cristiano Ronaldo, can not change Saudi Professional League entirely. He has failed to do this mission in MLS and I think it's unrealistic that he will be able to complete almost similar task in Saudi Arabia.