It will be a great relief if this feature (Offline maps) is implemented.
@Ivo, Here is a way to cache maps using Litchi. It is limited but if you have a Smart Controller you are supposed to be able to store DEM (Digital Elevation Maps) for future use when outside of Internet coverage.
This is from the Litchi faq page, and here is the link. Help - Litchi
11. I won’t have Internet access where I want to fly, will I still be able to see the maps?
If you cache the maps prior to the flight, you will be able to see them even when offline. To cache maps while connected to Internet, drag the map around where you are planning to fly, zoom in and zoom out. You can exit Litchi in between but avoid restarting the mobile device as it may clear the cache.
@Steve_Amerson
Hi!
Thanks a lot for the quick reply, but my idea is to save these cards, permanently, to be used when needed.
It is precisely for this reason that I wrote “great relief” 
P.S.
I’m using a phone. I.e. I don’t have a smart controller available.