Cornerstone - Yes. He has talent (we have seen from how he plays in Europe) and work ethic.
Franchise Player - I do not see it. When you look at a franchise player, they carry the team. They are the type of player you say "Cant win without him". I think he will be far less of a franchise player then Bosh (not to say Bosh was a legit franchise player). I think he will be solid and he will be able to carry the team at some points, but not a franchise player.
Who knows though? But whether he is a franchise player or not, he will make an impact. He has tons of talent, athletic ability, tons of experience playing against strong competition.