> it seems bogus that maps don't; this doesn't compile in Go if m is a map:

It does not seem bogus to me. Values in a map are not addressable for a good reasons. It allows more freedom in implementing a map. Arrays, on the other hand, are specified to be continuous in memory, hence the implementation is set in stone.

Also, non-existent items of a map return the zero value as specified. Now assume the map items are addressable. What exactly should happen if you refer to a field of a map item that is not in the map? Is there a possibility that is not surprising?