I brought up exactly the same issue in
DDC-764 a while back.
I don't understand the difficulty in allowing us to define a column in the superclass that Doctrine2 will use to to know what class name to use. Upon hydration, doctrine - in exactly the same way as with a discriminator map - will know which classes to instantiate. Class loading behaviour is basically identical.
This is proven by the fact that almost every single discriminator map I've seen to date looks like this:
"class_name" = "Class_Name"
"another_class" = "Another_Class"
Given this, I still maintain that discriminator maps are totally redundant and would love to hear more people sound off on this issue. This is a great dynamic feature with lots of merit. I think it deserves more research.