There's an AU in my head where Shen Yuan reads MDZS instead of PIDW (he doesn't realize it's danmei at first, or frankly until way later into it than most people would have), and ends up transmigrating into Madam Yu when he dies.
And like, he definitely hated Madam Yu just as much as he hated Shen Qingqiu on first read, but whereas Shen Yuan found Yue Qingyuan to be a reasonably cool guy, he thinks Jiang Fengmian is a major loser. With Yue Qingyuan there was some ambiguity as to why he let Shen Qingqiu run roughshod over him, plus he was a legendarily cool Sword Guy who famously sealed away the last demon emperor, even if PIDW never really gave him a chance to show off his skills in the story itself. But with Jiang Fengmian, he's just letting his wife terrorize everyone out of guilt over an old flame? Like not even a major transgression? Just that he liked someone else before he married her? And he's not even a strong cultivator!
Shen Yuan doesn't hate him or anything, but he's not interested in mending fences when he transmigrates either. He's perfectly happy to live in Madam Yu's separate house in the same compound, and immediately focus efforts on trying not to fuck those kids up so bad and also prevent his character's horrifying death. His chief annoyance is that he didn't transmigrate in sooner -- Wei Wuxian has already been brought into the family! And mistreated by the madam for a few years! Plus, Shen Yuan has to break the stupid OOC lock before he can stop outwardly treating that kid like trash.
But eventually he gets a mission to take the kids on a night hunt. He takes both boys plus Yanli along, because his system doesn't specify which kids, and having been a chronically ill kid in his past life he feels like it would just be mean to exclude Yanli if she's not having an actual flare up.
The skinner demon quest is actually pretty much the same as in PIDW. There's a rash of mysterious murders, and the cause turns out to be a malevolent ghost that has been possessing young women and wearing out their bodies with resentful energy until they literally fall apart. The main difference is that the skinner demon doesn't monologue, and the end confrontation is a lot more harrowing, and nobody gets tied up in fanservice ropes. Wei Wuxian helps Yu Ziyuan rescue Jiang Yanli, and Shen Yuan unlocks OOC mode and is finally able to start being nice to the protagonist.
He's also able to start doing things like change the training regimes for the Jiang sect disciples, offer constructive criticism (instead of just berating them), throw out all of the disciple whips, and dole out head pats and even the occasional hug (these kids are seriously touch-starved).
-He's gonna accidentally mess Jiang Cheng up worse in some respects, I think. Like in canon Jiang Cheng could at least console himself that even if his father didn't like him, his mother definitely preferred him to Wei Wuxian. Shen "blatantly picks favorites" Yuan is not going to offer that anymore, even if he is still going to be nice to and fond of Jiang Cheng.
-SY's internalized homophobia will manifest in whatever way is funniest, as per the laws governing his existence. I think he'd decide that he was going to be a helpful and tolerant Responsible Authority Figure about Wei Wuxian's unavoidable gayness. Thinking to himself, well, at least Lan Wangji's a respectable young man and pretty enough to be a woman. But given his own bad experiences with his sister's hardcore yaoi, plus wangxian's canonical cnc kink, he'd probably make it his mission to protect Wei Wuxian's dignity as the protagonist and health & safety as his own precious disciple by trying to encourage him to be a top. But like. Without ever actually mentioning sex either.
-Lots of metaphors that only convince Wei Wuxian that Madam Yu is worried he'll let himself get stabbed for some reason? Meanwhile everyone else in the sect is increasingly convinced that part of the continuing marital discord between the sect leader and his wife is due to Jiang Fengmian sucking in bed.
-The plot gets further derailed when Shen Yuan interferes in the death of Sect Leader Nie (Mingjue and Huaisang's dad). I'm not sure if we have a concrete chronological time for that death, but if we do I'm changing it to happen around when Wei Wuxian is like 13/14. Shen Yuan attends the event where Wen Ruohan provokes Sect Leader Nie into a qi deviation by accident, and kind of considers it a tactical blunder on his part (Sect Leader Nie's death is part of what pushes the Nie sect immediately into the confrontation with the Wen -- if it doesn't happen, will they hold off longer? Will the sunshot campaign be more difficult to organize?), but he can't just sit there and watch this guy qi deviate to death either. He's been planning to try and do something about the Nie sabres anyway, so he decides to consider it a test run and intervenes.
-Nie Mingjue's dad is basically Liu Qingge. Nie Qingge? Anyway, Team Steal Madam Yu From Her Loser Husband gains its first active member!
-Shen Yuan also accidentally wifebeams Wen Ruohan. Second member.