Please describe what the rule should do:

In Vue 3, v-model is always a shortcut for :modelValue="…" @update:modelValue="…". In Vue 2, those prop and event names could be customized with the model definition. A new ESLint rule would help with finding those deprecated model definitions in the codebase while upgrading to Vue 3. See also https://v3-migration.vuejs.org/breaking-changes/v-model.html

What category should the rule belong to?
[ ] Enforces code style (layout)
[x] Warns about a potential error (problem)
[ ] Suggests an alternate way of doing something (suggestion)
[ ] Other (please specify:)

Provide 2-3 code examples that this rule should warn about:

export default {
  model: {
    prop: 'list',
  }
}

export default defineComponent({
  model: {
    prop: 'list',
    event: 'update'
  }
})

export default Vue.extend({
  model: {
    event: 'update'
  }
})

Additional context
An additional allowVue3Compat boolean option (false by default) could help with transitioning to Vue 3:

When enabled, the rule would not report model definitions that match the Vue 3 usage:

export default defineComponent({
  model: {
    prop: 'foo-bar',
    event: 'update:foo-bar'
  }
})

After the Vue 3 migration, the option could be disabled again, the model definition could be deleted, and the v-model:foo="…" shorthand syntax could then be used without further changes.