I agree that it is complicated to define « high activity ». So, may be just report highest allocation activity (and source line location) at exit?
Highest activity could be e.g. a smoothed value of « number of allocations per second » (on a 1 sec or 5 sec rolling window?
As you said, may be it is too complicated? And we already have (manual) procedure in 1.8. My initial idea was to help the newbie in some simple way, but to have an idea of reasonable threshold warning values, we should have a passive instrumentation … which has no infrastructure and whose result could vary a lot.