The real problem I see is that multiple modules may want to use this hook, and they will probably all have a different idea of what the right value for $Data::Dumper::Freezer is.

Good point. I misunderstood how $Data::Dumper::Freezer worked. I thought you had to do something like this and it registered per package:

package Foo;

use Data::Dumper;
Data::Dumper->Freezer( "__FREEZE" );  # Incorrect!

sub __FREEZE {
  # custom class dump here
}
[download]

It looks like it's just a global, which is even worse. (Unless you want to use Data::Dumper objects, which can have a per D::D object freezer, but that's doesn't help either.)

As the discussion below suggests, I think Data::Dumper::Streamer comes closest with its FreezeClass handlers.