Biggest problem to swapping Arthur + 30m (40m?) for SMS is the difference in salaries, SMS is on 3.2m at Lazio and Arthur is on 5m at Juve until 2025. We'd have no problems giving SMS a bump, but Arthur would heavily disrupt Lazio's wage structure, can't see it happening. Because of that salary Arthurs suitors are a very small list of clubs like Arsenal or Newcastle, who're rich enough to not care about that salary and bad enough that he'd considerably improve them.
I don't think Lotito in the end cares that much were SMS ends up, if he gets paid enough to reshape the team and boost that horrible defensive lineup they have currently.