In T150887, we have added capability to add aliases for filetype: searches. We'd like to go through access logs for sites where such searches are used (commons, maybe enwiki and others?) and see if unsupported types are used with filetype: search and if we identify frequently used unsupported types, add support for them in the configuration.
We probably want to do it somewhere in January so we have enough data set to rely on.
Supported types are listed here: https://www.mediawiki.org/wiki/Help:CirrusSearch#filetype