The law has finally been finalized but they are still waiting for the local governments to modify some of the rules including the 180 day limit. Some localities will change it to less than 180 days. This review period is suppposed to end by the end of 2017. The registration of hosts will begin on March 15, 2018 and the law will come into effect on June 15, 2018.
The law requires you to report to the local government office by the 15th of every even month (Feb, Apr, Jun, Aug, Oct, Dec) the number of guests in the previous two months. It is my understanding that Airbnb will also block out your listing after reaching 180 days. My reading of what has been released by the government and other "experts" is that it will apply per room, but I am still not sure of that.
Anyway, that is where things stand now from what I have read in Japanese. I would say wait until after the start 2018 and then go down to your Local Hoken-sho to discuss with them. I will be going to visit mine in February after I return from a trip during all of January.
Anyway, I hope that helps a little bit.