DiGi, is Xenoglossia ever mentioned in passing as a joke or reference in official content? I think that'd be pretty cool.
Not that I can think of, but there's such an insane quantity of iM@S content in existence that it's difficult for any one person to consume it all (especially me these days - I have big blank areas of knowledge), so it's hard to imagine it doesn't exist anywhere.
That said, I kind of suspect Xenoglossia exists in a weird spot - whilst based on iM@S, I think a lot of the copyrights for the show itself (and it's merchandising) probably sit with Sunrise rather than Bamco, so it's probably a bit too much of a pain to negotiate the OK for even dumb gags.
I mean, bear in mind that Xenoglossia aired the same year as the original game was released on the 360, and at the point where the game was starting to roll out it's DLC catalogues. The original game only supported costume DLC, not new songs, so you'd have thought that
maybe they'd do a spot of cross-promotion with, say, the school uniform or even the flight suit (well, PE uniform if we're realistic) from the show, but nope.
The show wasn't actually referenced on the official iM@S site for a few years either, though it was added back on when they refreshed it back around (IIRC) the release of One for All. I have a bunch of different publications with timelines of the franchise history - listing things like character and drama CD series releases even - from between the release of 360 iM@S2 and One for All that fail to mention Xenoglossia at all as well. Infact, I think the only one I have which does (which, admittedly, is the most recent) is the English promotional pamphlet they made for conventions in Asia (AFA and the like).
That said, I don't think it's any ill-feelings from anyone at Bamco or anything - that Super Robot Wars cross-over BGBW mentioned was done as part of the wider iM@S 10th Anniversary celebrations, because they realised that they needed to give Xenoglossia props somewhere and it seemed like the most appropriate venue for it. That game has also had regular aniM@S content in the meantime, with an event based around the robot parody from the variety show episode of the series.
Okay, that's cool. Haha.
Speaking of which, I don't think I've ever seen the idols interact with each other in the game as much (minus Starlight Stage's scenes).
They didn't really interact much in the games based on the original generation iM@S. There was limited interaction in iM@S2, but it was only really between certain characters and certain members of Ryuuguu Komachi (who, remember, you could only produce in the special mode of PS3 iM@S2).
The thing to bear in mind is that in iM@S1, you were only producing between 1 and 3 idols (depending on your persistent Producer Rank and personal choice), not the entirety of the 765Pro All-Stars. Writing meaningful amounts of bespoke, voiced dialogue for any combination the 9/10 idols (Miki was only in 360, and Ami/Mami counted as one character originally) would have been insane. As such, you only really interacted with your units current Leader, or another character if you picked them for a specific event - whilst characters would appear on screen together, it was only with generic dialogue only addressed directly at the Producer, not each other.
iM@S2 was a similar situation, but as I say, since Ryuuguu were in there outside the realms of what you were producing, they included those characters within certain idols story paths where appropriate (Ami appears in Mami's story, I'm pretty sure Iori is in Yayoi's, etc), and there was stuff between the Ryuuguu members in the PS3 versions special mode.
With OFA and Platinum Stars, though, it's pretty clear that they've taken a degree of influence from the atmosphere of the TV anime, and with the game being written around the expectation the player will eventually be producing all of 765Pro, they felt free to include any of the characters whenever appropriate. Not that there's a ton of story content in Platinum Stars (that games kinda light on content, honestly), but OFA has some good stuff, especially in the DLC stories.
(Dearly Stars is different in that it's a bit more of a VN)