Code review comment for lp:~aacid/unity8/expandable_model_not_array

Specs don't state whether should be an array or a model [1], so this branch is doing the same as previews with 'widgets' being a model.

 * Did you perform an exploratory manual test run of the code change and any related functionality?
Let's wait a silo for that (requires integration), but code is fine
 * Did CI run pass? If not, please explain why.
Waiting CI

[1] https://docs.google.com/a/canonical.com/document/d/1NmiM4UCnJgf6IEawmfyTOHRNAA5ZGrqpyrPqPOibwc8/edit