Currently, it is only possible to get someones public key into DeltaChat if the person uses an AutoCrypt-capable MUA (i.e. DeltaChat). If there was an option to not only import private, but also public keys, wouldn’t that enable DeltaChat-users to communicate encrypted with non-Autocrypt-users in one to one chats?
A great deal of Delta-Chat users care about encryption. Therefore, a good quantity of them have been encrypting before and might even already went through the pain of importing the public keys of their corespondents and verifying their fingerprints and all that.
A big advantage of DC over other messenger I see is that it is not exclusive. What I mean is that one is not forced to use DC in order to communicate with DC-users. But this is broken when one wants to communicate encrypted: The non-DC user may need to install another mail-client or plugins into their thunderbird, which I think is no good UX.
This had been brought up before (for slightly different reasons): Using third-party key management (at least on android/mobile). Being able to optionally(!) use a 3rd party key-storage like a gpg-keyring on desktops or OpenKeyChain on Android would solve above problem, plus it would remove the necessity of importing and exporting keys. Just check the box and everything works.