1. This form is all about placing a block, but show title, edit title, machine name are shown first with theme and region chooser following.
Maybe we can switch those around to better faciliate the main use of this form: putting the block in the right region of the selected theme:
2. I'd expect the existing machine name pattern to be applied here, it would remove quite a bit UI noise.
3. We could enhance the hierachy a bit by grouping the title related elements in a fieldset. Maybe the checkbox should come first (still default to checked)
4. Submit buttons are left-aligned, this one should probably be blue as well. Maybe part of existing style guide work.