Bumping this thread because I find it really interesting, and because we have seen the trailer now and we know some parts that definitely haven't been retconned (like the 70 man battle).
I will make a risky bet, and I'll say that two important-ish characters from Shenmue II will be skipped: Joy and Yuan.
In the case of Joy, I have always suspected she is not in the original VF RPG scripts. She didn't appear on Shenmue beta trailers, nor in the chapter cards. As much as I like the character (much more than Nozomi indeed), I think she was a vehicle for having a kind of love interest in the second game, added after they realized Shenmue II would be a separate standalone game. And to serve as some kind of guidance to the player in the first story beats of Hong Kong. But if the anime portrays Nozomi, a second "love interest" in the same season might be too much. And, while in a different style, that role of "ambassador" to Hong Kong might perfectly be done by Xiuying herself, as a kind of hidden overseer to Ryo. Thus giving more punch to the reveal she is actually Master Tao.
As for the case of Yuan, the first reason is the trailer of the anime hints at being Lan Di himself the antagonist for the last Kowloon rooftop battle. That would mean Dou Niu's role would be downgraded to that of a secondary enemy, and that would make Yuan's role even less important (as a secondary enemy to the secondary one). Of course, also, in this time and age I wouldn't be surprised if the producers don't want to risk any controversy about the gender issues of the character, and/or if they don't feel confortable to portray a LGTB character as such a despicable antagonist.
If we get to talk into a possible second season and Shenmue 3 territory, I also think (or maybe hope) that they get rid of the "gangs" for good, and exchange them for CYM agents or something with a similar feeling of story progress. But I don't think they would retcon much else. I fully expect to keep (and expand) the mystical elements on an anime. And hope they tie the cave events with the following story much better than the games did (the bar isn't really high).
