I hope we won't see him ever again as a false 9. He was brilliant after he dropped back in midfield and Barca was able to control the game again.
I don't really see how speed is a criteria for a false 9 (at least not more so than in any other position in modern football). Only in the sense of having skills which enable the false 9 to hold on to the ball (be it through dribbling or using strength to hold the ball) is speed a true criteria as a false 9. In fact, one thing which have been imminently noticeable in Messi's change from right wing to false 9 is that he uses his speed a lot less; only in short bursts when dribbling is it truly vital. The two places where speed is a fundamental criteria in our system is on the flanks (full backs + wings) as those are the areas where large areas need to be covered through high tempo running.I think his workrate and eye for a killer pass makes him more suitable to play in midfield. He could come good as false 9 still, but I'd rather have a faster player there.