In the case of site-wide blocks, the list of pages should serve as a white-list of pages that can be edited.
The default value could be the noticeboards and arbitration pages (different per project), where the user can participate in, or appeal their case.
In case of a non-appealable ban, or abuse of these pages, these can be removed from the list.

Previously requested in a different context:

• T27400: Software should allow admins to give specific users permission to edit specific pages through blocks
• T119795: Add new user block option "can edit Wikipedia:Appealing_a_block"