IIUC, _source compression is available, but off by default, and it can be
turned on at either index creation, or by changing the mappings. However
IIUC as well, the compression setting needs to be set per-index-type?
Reading the index creation, as well as the mapping docs, there doesn't seem
to be a way to set compression to be on by default for all types that
appear, one would have to define it to be on for the expected types.
Would it seem (even) more useful to have a per-index top level setting to
make compression on by default rather than need to explicitly set it
per-type in the mappings?