Assuming that this is no longer going to be the default, it likely should either be public (so that people can use it by manually adding it to either their custom-built Gson or by registering it with the GsonModule) or removed entirely (if we think that it isn't a common enough use case to justify it being present in the library at all).

I assume that some user (possibly you?) had a use case for this at some point.  Do you have a feeling for how common this need might be?  My gut feel is not that common.