Model refactor: plan for impacts to analytics

[thekaveman]

• [x] Note what events/properties need updating
• [x] Plan for update for events going forward
• [ ] Plan for migration of old event data

[thekaveman]

Event/property updates documented in:

• [ ] #2233
• [ ] #2234
• [ ] #2235
• [ ] #2237
• [ ] #2238
• [ ] #2236