@Brett Barton that's a pretty old article. Yes, there are definitely a lot of airbnbs that are not "legal" airbnbs, but that doesn't mean Portland has not adopted code for them. Portland has a pretty strict code for airbnbs in residential zones, requiring a long term resident to live there for 275 days per year. This is a special "conditional use" that allows you to operate a nightly rental (which is an R2 use,......long term rentals are R1) which is not an use that is allowed in our residential zoning designations.
@Jim P., as @Neal Collins stated, the "hotel occupancy", which is allowed in the "retail and sales", which is part of the CM2 zone, would allow for nightly rentals. To fully be legal though, it requires to convert the building to an actual hotel. I've been through the process, it's doable, but likely not feasible for a project of small scale. You can always just throw it on airbnb, but you risk $5,000 per night fines.....not to mention the costs to furnish, manage and operate the unit.
In my opinion, airbnb from an ownership standpoint isn't much better than just a good old normal long term rental, unless there are unique/niche like features that allow your building to stand apart from all of the other (and we're talking thousands) airbnb units on the market.
Brett is right though, that part of town has a ton of demand. Putting your property to a higher and better use is definitely possible. We're hitting the end of this current development cycle, with construction costs, lowering rents and lending changes making new build projects less feasible, but the next building cycle shouldn't be too far down the road.