Ray Allen has that unique combination of being a natural shooter and being obsessed with shooting. I don't think Rondo could ever be close to the shooter Ray is because he is not a natural shooter and because his focus (which may also be obsessive) is on other aspects of his game.
I understand the point is that Rondo continue to improve, and it is inconceivable to me that he hasn't sought out Ray's advice or watched him to learn. Everyone, especially Rajon, knows that adding a reliable jumper to his game will make him unstoppable, but his greatness emanates first and foremost from his ball-handling, passing and leadership skills and that is where pririty #1 should continue to be in my opinion. He's almost a 'good enough' shooter already, and that is all he'll ever need to be given his skill set.
With relatively modest increase in minutes through the years, here are Rondo's per game assist averages for his career:
3.8
5.1
8.2
9.8
13.4