The 'signs' are, in my opinion that at a similar age he is streets ahead of say, Anderson in allot of the things that allot of us assumed that Anderson would have already developed (short passing, decision making, the weight of a pass, seemingly knowing when to play which pass, keeping and dictating tempo, shooting). He also seems to have two legs, which Anderson does not.
People will still harp on their thinking that Anderson has all of the potential in the world to be 'World Class', because he has shown glimpses. But then so has Cleverley. Though Cleverley, in what little we have seen in the first team seems to have, and add consistency in the midfield - even after months of layoff and lack of experience.
It seems that some don't want him to succeed as he isn't or hasn't shown at this level that he is a 'flair' player. However, I'd take my chances on Cleverley becoming more of a 'flair' player than I would on Anderson becoming consistent.