I had several false starts on this issue and always got too deep in describing the current implementation. So I'll post a half-baked list to get something down faster.

• How are/should fields handled, esp. special ones like type, dict, and superclass ones:
  • What should tp_traverse visit?
  • What code is in charge of initializing them? Zeroing them before initialization? Clearing them?
• Can an object outlive tp_clear?
• Can I rely on tp_clear being called?
• Which initialization/finalization APIs call a type's slots, and which ones bypass them?

etc.