There is a prototype by the author of the comic: https://github.com/saga-chat/saga-alpha
Demo is available at https://saga-chat.github.io/saga-alpha/
First of all, Delta Chat does not have replies, which are per-requisite for this feature: Reply to Message
As for the feature, offering two views for each chat and adding navigation elements to jump between “leafs” is too complicated. Delta Chat makes it very easy to create new chats and always sorts news messages below the last read message. In the chatlist new messages can be represented with a single number. “Glue” approach seems to be inspired by messengers like Slack or Discord, building upon the IRC model, where groups (or “channels”) are less dynamic and require more management, because even by default they have multiple user roles.