There kind-of will be a de-facto limit to a total super balance once the 296 tax comes into effect - and it will be $3m.Except there is no limit to the total super balance
Why I say this is that anyone who is caught by 296 would have to ask themselves the question: "Do I need to keep more than $3m in my super fund or are there more tax effective, and overall better after tax investment returns available by having the excess above $3M in a structure outside the super fund?".
If the answer to that question is "Yes, I can get a better after tax investment return outside super" then the super fund has been effectively capped - not by the government, but by the individual super fund member. (Another clever design element of this new tax).