This reminds me of Soundcloud a few years ago when they were giving away API access for free for unlimited plays but then were almost close to bankrupt and pretty much shut down all API plays. I ended up shutting down my 3rd party app then but not sure what's their API limits now. Twitter recently made huge changes to their API limits too which impacted a lot of 3rd party apps.
I hope Unsplash doesn't end up similar to those.