I initially posted this into questions forum, but I've been suggested to move it into ideas, so here I am…
How about making a Kustom android API so developers can build Kustom Weather Plugin apks with their favourite weather provider?
"update now" kustom-intent: retrieves the weather data for a given location.
"get X" kustom-intent: parses and returns the data (X) from the last retrieved data set for a given location
Of course, it's always more complex, but it's just an initial idea. Any other architecture (as the one already in use in Kustom Weather Plugin) will be OK.