IMO the main negative point for BBL is that their schedule is always clash with their own national team's fixtures. I find it weird that on one hand they play high profile series around nov-dec-jan (boxing day test etc) and also organise BBL.
The Australian cricket calendar was like that even before the introduction of the BBL. The test matches being played during Christmas-New Year vacations are a major revenue earner for Cricket Australia. However, this is problematic for those players, who participate in more than one format. And in terms of revenue, it works well for CA, because the test matches are played during the daytime and the BBL matches are mostly played during the evening. They are trying to maximize the revenue during peak season. Also, one argument is that there is not much overlap between the viewership for test and T20.
But, in search of revenue, the board itself is putting a lot of pressure on the players of Australia. Revenue is obviously going to be better because of this but really it is going to be bad for cricket.
You cannot expect a test player to play test cricket in the daytime and play t20 at night time on the same day. I am not saying that it is impossible but that is obviously not the optimal way to play for a player. They also have to really increase the salary of players in the BBL. Otherwise, it is going to lose a lot of popularity because great players are not going to be attracted. They should always first think about their players rather than the revenue.