Was there or will there ever be a Sub Rosa #23?
There is no Sub Rosa 23. This is the latest post that I’m aware of on “issue 23”: Did Sub Rosa publish anything after issue #22? - #11 by Ben_McFarland
That being said, Timothy Ferguson infered in Mythic Europe Magazine : Call for Submissions - #20 by Timothy_Ferguson that he had been supported by Sub Rosa. My guess is this would be the transfer of unpublished content (but it could be just advice), which would point in the direction that work stopped and won’t resume. This is just an informed speculation, and of course the authors might change their mind some time in the future and resurrect the fanzine. But the only currently active fanzine as far as I know is the one published by Timothy Ferguson.
It has been said, by Ben MacFarland IIRC, that the prospective content for issue #23 was finished quite some time ago, and in fact there were multiple articles for an issue #24 (which, again IIRC, was going to be northern themed). The hold up was on the art and publishing side. So there was definitely unpublished content to transfer, if that was desired by both parties (and okayed by authors).
As I understand it, some of the authors for Sub Rosa #23 pulled their pieces from there and submitted them to MEM1, with the blessing of the SR folks.
Speaking of…submissions are open for MEM2.