Yae Sakura seems to be the new character that most Genshin Impact players are talking about right now.
Interestingly enough, another Yae Sakura already exists in another miHoYo game (Honkai Impact 3rd). Her design and profession are nigh identical to the one found in Genshin Impact, which seems like an interesting homage from miHoYo. Most Genshin Impact players don't know about Honkai Impact 3rd, so it is an interesting fact to mention regarding the possibility of Yae Sakura being playable.
It's not unheard of for game developers to try and cross-promote their games with one another. While the Genshin Impact version of Yae Sakura is largely unknown, there is a strong possibility that miHoYo is testing the waters to add a character like her to Genshin Impact. It has been confirmed that Yae is a character involved in Genshin Impact, so there's a strong possibility that she can be playable.
Yae Sakura in Genshin Impact: Will she be a playable character?
As of right now, there are no leaks stating that Yae Sakura will be a playable character in Genshin Impact. There is no info on potential movesets or the like, so it's vital that players understand that this is a discussion on whether or not she'll likely be a playable character and not one on her potential use in the metagame.
One should never say never, as there is a strong possibility that a character like Yae Sakura can be made playable in Genshin Impact. She is playable in miHoYo's other game, Honkai Impact 3rd. While it isn't yet confirmed if both Yae Sakura versions are the same, there is a strong possibility for it to be so.
Yae Sakura is a well-liked character in Honkai Impact 3rd, so it wouldn't be a stretch to assume the Genshin Impact community will love her too. Sometimes, designing new characters takes up too much time or resources, so it's good to reuse old assets.
With Yae Sakura, most of her moves and designs can be directly borrowed from Honkai Impact 3rd and scaled up appropriately for Genshin Impact. She could still have changes made to her design, of course, but miHoYo wouldn't have to reinvent the wheel when using her pre-existing model as a baseline.
She will likely be important in some way
As Inazuma will be arriving soon in Genshin Impact, Yae Sakura will likely play some kind of role in the new region. She has already shown up in the official special program for the 1.5 update, and she has been mentioned by official Genshin Impact media.
She is apparently friends with Morax, the Geo Archon, and Baal, the Electro Archon. These are quite the friends to have in a game like Genshin Impact, so it wouldn't be surprising if she was involved in the Archon quest line at some point.
There will even be a location known as the Yae Publishing House in Inazuma. While it is not known if there is any correlation between the building and the character, there is a strong possibility that there is a connection between the two.
As far as other Genshin Impact info goes, Yae Sakura has invited Ayaka (an upcoming playable character) to her shrine as the first guest for 2020 in a tweet. It should be noted that the Genshin Impact version is sometimes named as Guuji Yae (with Guuji meaning chief priest in Japanese).
The main reason for miHoYo to include Yae Sakura in Genshin Impact would be to promote their older game, Honkai Impact 3rd. Other than sharing "Impact" in their titles, the two games are quite radically different from a gameplay perspective. However, that doesn't mean the demand to play both games doesn't exist.
As Genshin Impact is a far more popular game, including a Honkai Impact 3rd character could help bolster the latter game's recognition within the gaming community. At the end of the day, miHoYo is a video game company, and companies strive to make a profit. Any cute playable character will likely do that for Genshin Impact, but a good one from Honkai Impact 3rd could broaden the latter game's appeal.
Although Genshin Impact wouldn't get much directly from this exchange, it would help make Honkai Impact 3rd more popular. This, in turn, will make miHoYo more money. Several news sites covering Yae Sakura have covered that game, which is as good of a marketing strategy as one could hope for.
The most important part of being a cross-promotional character is the ability to see if it's a good business decision from miHoYo. If Yae Sakura is a massive success, then it's possible to see other good designs from Honkai Impact 3rd take shape in Genshin Impact. If the opposite is true, then miHoYo would know that there isn't much crossover appeal between the two games.