Random thoughts off the top of my head:

• Remove InstanceKey from logging APIs
• Rework re_data_store accordingly:
  • No auto-generated instance keys
  • No clustering key checks
  • Probably lots of tests to fix
• Rework re_query accordingly:
  • Make it archetype-less, key-less, PoV-less, join-less
  • Do we still need re_query at all? If we do, it can be vastly simplified
  • Probably lots of tests to fix
• Rework re_query_cache accordingly:
  • Make it archetype-less, key-less, PoV-less, join-less
  • Probably lots of tests to fix
• Update every downstream crates accordingly:
  • Stuff driven by InstanceKey (e.g. hover) should be driven by
  • Visualizers
• Introduce a new Rerun-agnostic Identifier component
  • Just a u64 for now, until we have datatype conversions
  • Doesn't do any magic, just a way to have persistent IDs to drive visualizer features

This is not an exhaustive list, InstanceKeys are everywhere.

It will be way simpler to build all of this on the side while keeping the existing stuff untouched and then switch everything, rather than living across two worlds for who knows how long.
I.e. build all of that stuff bite-size pieces in parallel, and only start removing the old stuff when things are in place.