Well stated, even when runescape'api' could be tightly locked down - they would soon encounter precisely the OSRS gold exact same problem blizzard experiences. Lets say you would like to prevent plugins that auto-draw on the floor during boss fights, however the'draw x tile' API can also be used innocently - you can't simply remove the API callback without breaking, and let us say manual floor markers.
Blizzard haven't really ever banned addons, with the exclusion of some addons which were trying to conceal behind a subscription based cover wall. Short of anti-virus like code inside the game which finds forbidden origin code, theres nothing they can do except split the API.
back in WoTLK there was a boss mod addon called AVR (augmented virtual reality), it would draw the screen in real time to signify the radius of boss mechanisms, where to stand, where not to stand. It was an unbelievable feat of technology but blizzard's only option was to cripple the minimap scope API that it relied on - that is why range assessing addons in WoW are scuffed for this day.
They can't purchase it because it is can you buy runescape gold open source and has been contributed to by hundreds if not thousands of people who all have ownership rights of the parts of this code. They can however just make their particular build they maintain and discharge without paying a thing, since it is open source.
Yep I really don't get why they don't do this , I wish they would put the official link on the website so people would not accidentally go to the wrong one.