Here is the problem Haley, *I* am assuming that the municipal law in Shibuya doesn't affect standalone structures, but honestly, *I* don't know, my Japanese isn't that good and I have my doubts that yours is either. It's a risk. If the law specifically for Shibuya is *ALL* rentals, you are still at risk. It might not happen before your trip or even during your trip, but you are taking a risk and one I know I would not want to take if I had other options.
And quite honestly, it seems to me a little odd that you have recommended AirBnBs in Tokyo to another user when you 1) don't know the restrictions in specific municipalities and what will or will not apply to rentals (and I don't know about you, but I would feel terrible if I recommended something and then the person got completely screwed over and either had a cancellation a few days out or ended up with a visit from the police.) and 2) you've never been to Japan. You don't even know if your AirBnB is going to work out or how happy you will actually be since you've never been there. Places, even places with good reviews, can be disappointing. Someone I met through Japan Guide just came back saying how much they didn't like their AirBnB on Naoshima. They talked about it not being terribly clean. I am sure they picked somewhere with decent reviews.
Saying an AirBnB is in Shibuya and near a station can mean a lot of things. You could be near Sasazuka Station on the Keio line or Yoyogi-Uehara Station on the Odakyu. Both are I am sure perfectly safe and lovely locations, but they're not the same thing as being in what most tourists think of as Shibuya, though both are in Shibuya and are stations in Shibuya. In my experience in the more touristy parts of Shibuya, I don't remember any stand alone houses, just lots of shops, restaurants, and apartments. Sasazuka is only 11 minutes from Shibuya 109 by train... if you make the right connections and don't get lost making said connections.
I have stayed in Setagaya-ku in a house in Meidaimae, and while if I was going to live in Tokyo, that would be a top area, it's not all that convenient as a tourist and I stayed there because my friend was letting me stay there for free. It's like I've also stayed out in Nishi Kokubunji and Nishi Ogikubo, which are also nice areas, but not somewhere I would pay to stay unless I was looking at somewhere to live in Tokyo.
Last June, my friends in Osaka told me people in Kansai were pissed about suitcases on local transport. And I've personally seen some pretty crazy stuff, like the Australian family wanting to bring 2 36"+ suitcases on a local Kyoto bus to get to their AirBnB, and that is just really disruptive for people who live in a city. Most local trains aren't made for taking large bags on and unless you are traveling is the middle of the day, local trains can get pretty crowded. May 2018, there are now signs up talking about fines, who is to say that by Spring of next year there will not be discussions of fines for taking bags on local transport in Tokyo.
Since you're not looking to travel until close to a year from now, I would personally wait until at least the end of the Summer before booking anything with AirBnB just to see how everything plays out. Again, I read the AirBnB press release, and while everyone is getting full refunds and help making new reservations and a credit towards an AirBnB experience, getting anything more than that is up to the discretion of AirBnB and I would want to know how this is going to play out before using their service or recommending it to others.