I'll chime in confirming as well. I have 3 roms. 1 main on fed side, and then 1 fed and 1 klink just for farming this mission. I could usually count on my klink getting this once or twice a week. My main at least once a week. They've disappeared completely. I check hourly when I'm on at both Tau Dewa and the Command center. I haven't even gotten a regular recruitment mission for just fed aligned species either. Maybe 1 for a human on fed side. But 0 Romulan missions since the update. Hope it's just a bug with the timing. This was a good stable source of income for me, as well as allowing me to outfit my main and alts with full bridge crews. That it's rare shouldn't make any difference. I see Rare missions all the time multiple times a week for other assignments like Science and Eng and what not. It's not THAT rare, nor should it be.
I haven't gotten one lately either. It may have been since s9.5 dropped, but I'm almost certain I did one using the new doff UI (don't hold me to this though, it may well have been on one of my other non-Romulan characters and I'm misremembering). I've seen the allied recruitment mission come up two or three times, but no Romulan. Romulan always seemed more common than those for me, despite what others claimed about it being rare.
I don't remember ever going more than a week without getting one. I think it's bugged, I filed a ticket last night.
Aside from the rarity, the problem I have with this assignment is that I can flag it on 1 character and then when I log into any other characters to flag it, it won't appear. It's as if I'm only allowed 1 copy of it at a time. As far as race and commendation ranks, all are the same. I can't think of any other variables that might affect it's presence.