It is mentioned in the AMA on reddit, but not as clearly as during his last interview with Famitsu.
Taken from the interview he did for Famitsu:
Famitsu: In Shenmue 2, it was possible to walk through many towns over a wide area of Hong Kong, wasnt it.
Yu Suzuki: Actually, at that time, I had decided that for Shenmue 3 I would delve in more deeply.
Famitsu: More deeply?
Yu Suzuki: Yes. People might expect that the open world would be made even broader, but in contrast to that, I will focus on depth. For example, for the case of 100 characters, splitting the development budget among them would limit the elements that could be incorporated into each character.
Famitsu: Thats true, it would make it harder to create each with detail.
Yu Suzuki: However, if we reduce the number to 10 characters, a lot of possibilities are opened up. The amount of conversation could be increased 10 times, or detailed A.I. provided for each character. As a result, conversations could be much richer. As an example, in Shenmue 3 the person that Ryo will speak with most is Shen Hua, so I want to portray her with depth. I envisage an approach where, by settings parameters for Shen Hua, on-going conversations with her will influence events such as changing her attitude, or changing the way that quests relating to her unfold.
Famitsu: I see. I think a lot of support for Shenmue comes not from just the realistic towns, but from the realism of the people inhabiting it. From what you have described, this realism will be further increased, and the world will feel even more human.
Yu Suzuki: Yes. In Shenmue this time I will be focusing particularly on digging down further on such internal aspects.
Famitsu: This is your vision for the new Shenmue, isnt it.
Yu Suzuki: Of course, thats not to say it will not be open world. Stretch goals will allow the town(s) to be expanded. However, what I would like to try first is to develop something that everyone has not anticipated; a deep Shenmue world.
http://www.shenmuedojo.net/forum/viewtopic.php?p=1089690#p1089690
I strongly encourage everyone here to read the rest of the interview. There's a lot of info and insight in it, and it gives a clearer idea as to what to expect from the game, the kickstarter and its stretch goals.
Special nod and thanks to ShenmueDojo, and to Axm and Switch in particular, for translating this from japanese.