Where can we tie a generic Field UI?

I think the IA decision to put Field UI configuration pages into the context of the fieldable entity is wrong.

Here are two reasons why it won't work out that way:

1. Fieldable comments: If comments are fieldable, then we want to create separate field bundles per-content-type. So where will the field management pages for comments live?
2. Fieldable fields: Where is that supposed to live?

Why did we implement that Field UI IA in the first place?