The rate of his physical decline and the question marks over Barca's ability to cater for it are so similar to Ronaldinho's case. Of course, Messi is a far greater player but the evolution of football is that when 1 team has a style that gets the best out of the team via sub-servicing a star player and the signs are showing that the player in question is under strain, at what point is it best to keep the faith or try something new?
Ronaldinho, of course, had many off field problems and general attitude issues but Messi, for all his professionalism is becoming embroiled in legal off field issues also. He has won everything there is to win, is his hunger and appetite still the same? Will it remain so for the foreseeable future etc. He appears to have lost that acceleration he once had almost completely, in turn he is stronger now and this is the main asset to successfully completing his dribbles now. The speed in decline of his work rate, acceleration etc is such that playing into his mid thirties looks unlikely, in Europe perhaps without reinvention.
And suddenly there are more and more issues, more debate, more concerns. Now I'm not suggesting Messi is done or anything daft like that. The goals and impact he has still far outweighs all but 1 player in the world right now so a fair grasp on the real context is needed also but there will come a time when all things need to be considered ie life after Messi.
With Munir, Rafinha, Suarez, Neymar, Dongou, Seung-Woo etc evolution is a continual process at Barca and 1 day Messi's time will be up. That day may be approaching much faster than any of us could have imagined just 1 year ago.