Hypotheticals putting me off interstate travel:
• Flying home is out of the question.
• Could extend stay or find alternate accomodation, but am I under any moral/legal obligation to disclose my COVID status and risk being turned away?
• Are hotels obligated to let me stay to isolate? What happens in an Airbnb and the place is double booked?
You do what you to if you get sick - you stay in bed in your hotel room / minimise contact with the outside world and you extend your stay if you need to.
Hotels or Air Bnbs are not obligated to extend your stay - this is something you would have to arrange yourself with alternative providers if required.
Yes it would be highly irresponsible to get on a plane with covid and possibly even illegal.
Fortunately most people have fairly mild cases so I image you may only need to extend your stay by a few days in the worst case.