It is relatively common need to spawn multiple instances of some blocks of core modules.

For example, having two (different?) user login blocks, or most recent nodes/comments listings (though that's probably not worth the effort => Views), etc.

So it might be worth to add a block_api_core sub-module, which basically does nothing else than to rewrite some of the most common core blocks into Block API block types, so users can create multiple instances of them.

Most likely not working on this myself, but wanted to create a feature request for this nevertheless.