#2 Prolong his career
Lionel Messi has never been reliant on his pace, but the Argentine's burst over his first five yards has been the cornerstone of his dribbling magic. He may be the best footballer in the world, but the aging process will rob him off this crucial asset, however gradual.
Messi's rival, Cristiano Ronaldo has already made his peace with his lack of pace and moved to a central role, while accepting being rested by Zidane, in a bid to maximize his effectiveness. Messi will have to accept a similar shift - continue in a forward role, and soon enough the lack of a burst of pace might allow defenders to mark him ever more so tightly.
A move into midfield would afford Messi to rely more on his vision and passing ability - abilities that do not reduce however much you age (see: Totti, Francesco). There's greater space on offer in midfield when compared to the forward line, and it would be conceivable that Messi could play in this position for another decade with ease.