Lillard is already 22 that hinders his ceiling somewhat ... he'll at least have some incremental growth going forward -- the biggest strides he'll take are probably just becoming more consistent. But counting on him to become a "superstar" (like a top ten guy in the league and in the conversation for MVP) is probably pretty slim.
Chances are if this team is ever going to have a shot becoming a title contender with this core of players (LMA, Batum, Lillard) they're going to need to be more like those early aughts Pistons teams vs. the traditional "2/3 superstars and roleplayers" model. To me that means that even if Lillard turns into a top 5 guy at his position, this team still needs another near all-star caliber acquisition to bolster this team.