Improve the “historical data” functionality (within the app and/or the web user interface itself - not an API to another app) to allow the user to download historical data. Currently the data can be viewed but not downloaded. This would allow analysis of the data (in other applications for example).
Allowing the user to select a date range to download data would be nice to have.
Note that the current “history” functionality appears to be limited to a day-by-day scrolling (in the app) and a max/min over a pre-defined date range (in the web interface).
Note also that the IFTTT functionality that exists is limited to downloading live data (i.e. not historical data).
There is another (year old) feature request very similar to this, but this request is specifically to add this feature to a user-accessible interface.