From a usability perspective, it's absolutely critical.

The goal of this refactoring was to allow models to receive, as constructor
arguments, the  constraint objects or other transformations that the user
wishes to place on model parameters, with the norm constraint as a special
case.

The user knows (or chooses in some manner) the value of the constraint.
What he doesn't know without careful thought about the type of layer and
its geometry (and honestly shouldn't have to know) is which axes correspond
to the number of filters versus other dimensions. I _suppose_ that
overriding the axes in the constructor may be useful, but in most cases
this is information that the model should provide.

To put a finer point on it, the idea was to deprecate max_col_norm in favor
of something more general, not keep the interface while introducing more
complexity underlying its implementation.