subgroups?

I need to build my distribution profile in anticipation of the subgroups module. I see that in D7 hook_schema_alter was used to add a 'parent' field to the group entity table. However I read somewhere that altering tables is regarded as bad practice in Drupal.

Does this mean that subgroups will be implemented with an entity reference 'parent' field, perhaps with custom validation to prevent circular references? Won't that be very simple? Can I contribute the core of it so that I have something to build on?