Currently the classes in model.py use the underlying protobuf _pb object for read-only properties instead of the proto-plus object.

This avoided some possible breaking changes, but was mostly done to expedite the transition to the microgenerator.

There are some benefits to using proto-plus that would be worth taking advantage of. Most importantly, timestamp well-known types are properly translated into a datetime-like object with proto-plus.

Why now?

There are some breaking changes in the latest generated clients due to googleapis/gapic-generator-python#595

• https://github.com/googleapis/python-bigquery/pull/316/files#diff-daa390c4795c10c42d5e8cec48f5339c

If we need to make a breaking change for these changes, we might as well update the classes to support the latest versions.