While building all of airbnb is hard, let's look at a clone like outdoorsy, which is airbnb for rv's. It was very functional a year ago, and i doubt if it took a decent team more than a few months. The lore of how to build for scale is now far more widely known, and anyone doing dd on a codebase can figure out if scaling a monolith will require a full scorched earth or whether its has nice modularity allowing it to scale in flight, and/or get to fairly high scale with light application of autoscale shards and now commonplace cloud methodology.

The issue is brand and usability, and wordle has it. The method for social sharing is genius, i think. A great example of privacy by design (sharing is explicit and through an image not a share button going who knows where).