I actually sent in an application to Rare specifically about this topic just yesterday, crossing my fingers :P
Nice to see this topic coming up in the forums ^^
Every game should have APIs in 2018 in my opinion, no matter how small or big.
There is no single source where good ideas come from, everyone can be a contributor if we enabled everyone to build on a great base, there's no stopping the innovative things that will come out.
Sooner or later people reverse engineer things, given enough demand. If there's an official API set, people would rather focus on building on there.
Just look at Pokemon Go, it had an awesome dev community in the beginning but they had to reverse engineer the whole thing.
Some devs used their skills for cheating, some devs used their skills for cool apps and add-ons. For example: I created an app that connected to my smart bulbs and whenever a gym battle was going at the nearest gym to my place, it would flash and then when the battle is done, it would take the color of the victorious team.
They chose to battle all devs instead of trying to implement anti-cheat measures...
Overwatch didn't (and I guess still doesn't) have an official API, so we had to scrape their stats website which, in turn, lead to unregulated traffic and load to their systems.
This kind of list goes on and on. Not having official APIs is not time or resource saving, it's actually extra headache.
League of Legends, World of Warcraft, Destiny 2, Eve Online, Guild Wars, Steam, Mixer, Xbox Live, Twitch all have various APIs and there's a massive ecosystem around them which provide value to the players & users. There are tons of APIs out there that I can't recount here, which we can integrate things to.
Just imagine how cool IoT Sea of Thieves merch would be.
Apart from stats, achievements, commendations, character & asset management, game info (items, merchants, factions, mobs etc.), I think real time event triggers would be an awesome addition as well.
I get excited just thinking about the possibilities :)