I suspect it will come down how successful the treasury is in their goal to minimize the burden on the real-estate industry.Too much still is not known to know how big a burden these new regulations will be. 

Owner was motivated and work needed was minimal How did you find this deal and how did you negotiate it?

My guess is that locals/ council members feel as though the ratio of STRs to owner occupied homes is out of whack there, which would indeed indicate market saturation/ a tipping point in regulation.

These two things indicate to me that you want the first as a starting point that is informational in nature.

When sewage backs up in multiple locations, that indicates the main is clogged.

If you are over for a bill period it's likely minimal and then tenant can probably absorb that amount in the monthly payment.

As indicated, I know multi-unit properties that did get F/F financing with an ADU.

If your house is a 1950s with minimal updates in a C/D area, $800/month is not unreasonable given the 1 bathroom and lack of updates. 

If anything, it'll indicate how much of a steal they currently have. 

You could add a couple hundred dollars income every month with minimal effort.