I'm about to be controversial! (I think.) At the outset I have to say I love Svetlana. She's such a distinctive character who owns every scene she's in, is obviously a huge support to Ilya without ever losing herslef in the role of that support, she's terrifying, she'll eat you for breakfast in the daintiest most menacing way possible and you'll thank her for the privilege afterwards. I'm preaching to the choir, we all love Sveta.
But! I do think her particular place in the narrative and who she is to Ilya opens up some interesting avenues wrt her feelings about Shane. I've generally seen her in fic as being aggressively supportive of their relationship, though I've read a couple where she is uneasy about the move to Ottawa (reasonably so!) and one fantastic one where she straight up dislikes Shane because she doesn't think he's doing enough for Ilya.
There's plenty of jealous!Shane, but what I'd love to see more of is jealous!Svetlana. Not jealous in the romantic sense--we see pretty clearly that Ilya's not like that for her--but Svetlana reckoning with the presence of Shane in Ilya's life and what that means for her place in it.
The scene with Sasha in Sochi is fascinating to me. She tows Ilya along like he has no say in what's happening, she tosses Sasha at him like she's ordering for Ilya at a restaurant, and then even with Ilya's old squeeze in the room splaying his body out for Ilya in the exact way that she clearly wanted, she still monopolises Ilya's attention. There's a benevolent peremptory presumptuousness to her behaviour that I love: she's clearly used to having to muscle him into things that are for his own good because he won't reach for them himself, and I think it's so juicy that she's used to having the sole right to do that for him.
How would she react to having that exclusivity taken away? Ilya very obviously lets only her behind his walls, until Shane bulldozes his way past them in Tampa. I think it's interesting to examine how Svetlana would react to losing that primacy with Ilya--it's not jealousy in a romantic or sexual sense, but Ilya's never had anyone like Shane before,and that would be an adjustment for Svetlana, I think. She's not just going from being Ilya's first call to his second call: she's going from being his only call to his second; from being the only one behind the wall to sharing that space for the first time. From having the surety that she can walk into Ilya's house to surprise him, in whatever way she wants, to having to reckon with Shane or even having to check with him first. Especially given the much closer relationship in the show--I can't imagine that show!Svetlana meets Shane the day before their wedding, and given their closeness, Shane forbidding Ilya from telling Svetlana would be a lot less excusable than it was in the book.
We don't know much about Svetlana outside of Ilya, so we don't know how strong her support system is without him, but there's room to wonder how crucial his availability for her, for lack of a better phrasing, is, and how she'd grapple with no longer being his first priority. To be clear, she knows, and we know, thst the worry is baseless and that Ilya would drop everything for her. But there's a security in being First and it's interesting to wonder how Svetlana would deal with losing that, and how that would affect how she interacts with Shane.
There's also the hockey of it all--Ilya is surrounded by it, but for Svetlana, he's very likely to be one of the most hockey-intelligent people in her life and they're clearly accustomed to constantly talking puck with each other. Now, there's Shane: famously high hockey IQ but can also engage directly with Ilya as a player and is probably the only person in the world who can, who has access to Ilya's hockey brain in a way Svetlana never will. This is kind of a mirror of my headcanon for Hayden's jealousy of Ilya: being supplanted as the best friend's First Hockey Person.
Honestly I just like to think about what it would look like if the completely baseless jealousy went both ways. I think they would eventually grow to like each other, and of course they're both ultimately grateful for each other's presnece in Ilya's life because it ensures his well being and happiness. Any possessive feelings would be subsumed by their love for him, but Shane obviously has some jealousy to navigate through to get to that point and it would be an interesting dynamic for Svetlana to have to navigate that as well.