My co-worker is designing a schema where most entities (like contacts, quotes, tasks) inherit from an "entity" table, which keeps track of things like which tenant owns the entity, and chagnes to the entity. This is similar to VTiger CRM's schema.

Is this a terrible idea? What should I tell him the problems are?

ENTITY
id PK
tenant FK TENANT
version
draft
deleted

ENTITYCHANGE
entityId PK FK ENTITY
version PK FK ENTITY
createdBy
createdAt
fieldName
fromValue
toValue

CONTACT
id PK FK ENTITY
name
[other contact fields]

QUOTE
id PK FK ENTITY
contactId FK CONTACT
[other quote fields]