@BeAware complete interoperability would indeed be a wonderful feature, but the simple adage holds true: the first 90% takes 10% of the time, the remaining 10% takes 90% of the time, and is also not very fun to do 😁
Also, what does "complete interoperability" mean when different software do different things? Anything that is a superset of #ActivityPub is easy (e.g. upvotes/downvotes are a superset of AP Likes), but its very hard the other way (#nodebb doesn't do post visibility like Mastodon)