Since Ken and Koromaru have been announced I went back and watched the persona stalker videos, I happened to find an interesting image. Just after mentioning P4U2 a silhouette appears on screen with 4 personae on, Izanagi, Jiraiya, then less noticeably Cerberus and... Orpheus. I don't speak Japanese so I can't tell 100% that it is indeed for Ultimax. BUT given the odd coupling of personae, realistically after the announcement of Ken and Koro, all 3 personae are in game except Orpheus. Theo was announced with Ken and Koro as in game. Therefore given he is the only character besides Aigis and Liz with the disposition to summon Orpheus (other than P3MC) it's a good indication he is playable. So if anyone can speak Japanese the video may not discuss the image but could be a good jumping point for discussion. I personally think there are 4 routes of Orpheus being used in game, Theo helping Liz (or option 2 canonizing FeMC and doing the same as Liz), P3MC playable character/ appearance or a story sequence uses it via, Aigis/Liz/Theo/Yu (or even an antagonist).
Posted image, but for some reason won't let me paste any text (sorry first post) anywhere so can't link the vid, sorry! Again this 100% speculation but that image was a weird grouping in, which most likely is not coincidence, would just like some thoughts on it! :D