They are possible but they are not possible to make per formant compared to the alternative.
Google falls under the "absurd amount of money" camp.
> Protocol Buffers have performance implications for query
processing. First, we always have to fetch entire Protocol Buffer columns from Spanner, even when we are only interested in a small subset of fields.
There are a number of performance costs documented in the paper. Simply because you can solve it via money doesn't mean it works for all situations.