Relatedly, most of the author's concerns are solved by wrapping things in a message.

> oneof fields can’t be repeated.

Wrap oneof field in message which can be repeated

> map fields cannot be repeated.

Wrap in message which can contain repeated fields

> map values cannot be other maps.

Wrap map in message which can be a value

Perhaps this is slightly inconvenient/un-ergonomic, but the author is positioning these things as "protos fundamentally can't do this".

To clarify. Protobuf’s simplest change is adding a field to a message so wrapping maps of maps, maps of fields, oneof fields into a message makes these play to its strengths. It feels like over engineering to turn your Inventory map of items into a Inventory message, but you will be grateful for it when you need a capacity field later.