One of the very surprising things about Shang-Chi and The Legend of The Ten Rings is how uninterested it is in the greater Marvel Cinematic Universe. This is by no means a bad thing, and these origin movies need to be their own thing before they are part of the MCU. It makes it an extremely approachable movie for someone who might be dipping their toes into the MCU and could be one of the movies that really helps convert fans that might be on the fence. There are some MCU universe-building hints, and one of them is much more subtle than Wong and The Abomination fighting. However, to get into it, we're going to need to talk spoilers not just for Shang-Chi, but for Black Widow as well. If you haven't seen both of these movies, then don't look beyond the spoiler graphic, but if so, let's talk about what some more subtle worldbuilding could mean.
So let's cover the ending of Black Widow first. The whole story of Black Widow is that they are trying to free the Widows from chemical brainwashing and, at the end of the movie, there is a large group of Widows that have been freed and enough of the serum left that Milena could make more. The Widows come back for Yelena, and the last time Natasha sees her family in the film (that we know of), Yelena and the others are going off to find the other Widows still undercover all over the world to free them. We find out in an after-credits scene that Yelena is working for Contessa Valentina, but we don't know what happened to the other Widows. Then we see another Widow in Shang-Chi. When Shang-Chi and Katy arrive at Xialing's fighting club, we see a woman fighting a man who appears to have fire powers, possibly Extremis-related powers. We saw a former Widow fighting Natasha during the office fight in Black Widow played by Jade Xu. She is called Helen in the movie, and it is a blink-and-you-miss-it type of cameo. During the final credits scene in Shang-Chi, we see that Xialing has taken over the Ten Rings, and a group of women is fighting. It's currently unclear if Helen is in that fight scene, but she very well could be part of the Ten Rings.
The question becomes; what happened to all of those Widows? After the events of Black Widow and with all of them being freed after years of not even having control of their own lives, they are very vulnerable to manipulation. Yelena explained that the vest she bought was the first piece of clothing that she ever chose for herself. All of these women are incredibly deadly and well-trained, but they could easily be taken advantage of by someone. Yelena is working for Valentina, is Helen working for Xialing? She could be, and there is a chance that more Widows could join up in different organizations all over the Marvel Cinematic Universe. Someone like Valetina or Xialing having access to fully trained assassins that are just ripe to be taken advantage of, even if that is not the intention, is bad news for everyone in the MCU.
The question of the freed Widows and where and who they end up working for might be one of those things that Marvel never really decides to explore in the long run, but it is interesting. There is a current of female empowerment running through both of these movies. Black Widow is much more on the nose, but Xialing in Shang-Chi built her fighting empire and taught herself to fight because her father kept her out of the Ten Rings. Now that the Ten Rings is under her control, she can bring in someone like Helen as a fighter. However, to cover the empowerment angle, you also need to talk about what happens when these women are put out into the world. They could fall into the hands of someone like Xialing, who doesn't seem to be a bad person aside from wanting some power. Or they could fall into the hands of Valentina, who is not being set up as a nice person. There are a lot of other Widows running around out there in the Marvel Cinematic Universe, and the person or persons who manage to recruit most of them is going to have a massive tactical advantage for good or for ill.
For now, Helen is a background character in the office fight in Black Widow, and in a brief cameo in Shang-Chi, the question of the freed Widows and what they are doing remains up in the air. It's going to be interesting to see if Marvel ever really addresses them or if they are going to hang out in the background. Are we ever going to see how easy it would be for someone like Valentina to take advantage of someone like Yelena when they are that vulnerable? We'll have to see how things turn out later down the line.