Hey it's Breakthru! Almost.
I don't know if it was intentional, but in the original, after you clear a line, they bunch up together to allow you to get more moves. Clearing about 95% (I forget the real amount, been awhile) gave you a new stage.
Adding that plus what Admiral R mentioned would make this last quite awhile longer.
Even if you don't make them 'bunch up' making a cutoff point for advancment would help this a lot.