BotW Zelda is one of the more annoying incarnations of Zelda, and that would be my biggest concern about her being playable. She needs to chill the **** out and stop being so whiny (ZELDA TRIANGLE LIP NEEDS TO SUPPRESS HER EMOTIONS LIKE LINK HAHAHAHA), otherwise it's really going to be distracting from the gameplay. I'm worried about how much screentime she's going to get already, because of how irritating she was in BotW and that was just in the memories.
Only thing I can say though, is that usually a character cutting their hair off like that is symbolic of a transformation of ideals or worldly outlook (think Zuko from Avatar; or Mulan too I guess), so if that signifies anything, maybe she'll have grown up a bit between the time of BotW and BotW2.
I didn't really like the incarnation of Zelda in ST either, but some of the co-op gameplay was the start of some really unique puzzles, if they wanted to polish up that execution, I'm sure it'd be okay. But yeah, she can't be the main player character, or it just wouldn't feel right.