What if instead of API's for data sets, we simply placed a sqlite file onto a web server as a static asset, so you could just periodically do a GET and have a local copy.
replies(4):
Devdocs does something similar, but there you request to download the payload manually, and the data is still browsable online without you having to download all of it. The data is also split in a convenient manner (by programming language/library). In other words, you can download individual parts. The UI also remains available offline, which is pretty cool.