XMetaL 13 Integration for SDL Tridion Docs?


I'm looking for information on if or when SDL Tridion Docs will support XMetaL 13? We are currently using XMetaL 12. I've been told XMetaL 13 has a feature that allows us to set attributes based on a subject scheme which is functionality that we'd like to use. However XMetaL 13 is not currently supported, hence the question if or when XMetaL 13 will be supported in SDL Tridion Docs.

Thanks in advance for any info.