In order to support communication between devices which are not connected to a reliable network, especially in situations such as government shutdowns of Internet service (as often occurs during civil unrest in certain countries) or sudden infrastructure failures, which can be unplanned and users might not have ways to share new encryption keys to migrate to Bluetooth messaging apps, it would be good for Delta Chat to support direct communication with nearby devices, such as by Bluetooth or Wi-Fi Direct. In order to lessen the burden of support on the Delta Chat providers, it might be possible to wrap up a chatmail server into an Android application that also helps users set up Wi-Fi Direct. The main DeltaChat-side problem would be to allow the users to temporarily connect to this direct chatmail server, and return to the global email network once the network has been stabilized. Additionally, it would be useful to allow multiple servers to recieve the messages, so that in case one person’s chatmail server goes down they are still able to recieve the messages from other people’s chatmail server. This could also potentially allow relaying messages for longer than the distance provided by Wi-Fi Direct or Bluetooth. Finally, it might be difficult to set up a proper connection over Wi-Fi Direct or Bluetooth, especially on sandboxed operating systems like Android or iOS. On Linux, it should definitely be possible to set up an IP over Bluetooth connection.
I think the existing messengers that work this way are enough.
Sure, It’d be nice to have, but not worth the implementation and maintenance effort (speaking as a random dude on the internet).
There was an experiment for a companion app for the yggmail network: https://github.com/deltachat/AndroidYggmail
So the idea of companion app that emulates a mail server and does sth different under the hood is certainly feasible.
On iOS apps can not run in the background, so there it would be harder and require tricks like jailbreak or playing a video or music to stay in the background.
Yggdrasil network also already works over apples flavour of direct wifi on macOS: https://yggdrasil-network.github.io/2019/08/19/awdl.html
Yggdrasil looks pretty interesting, actually. I hadn’t thought such a unified framework existed, so one of my ideas was to implement one myself. It’s nice to see that there are other people working on bridging existing p2p networking systems.