Unfortunately, no, there is no current way to ship a console app and have it run inside the system terminal app. You would need to ship your own version of the terminal in your app's package, and run your app inside it.
Dan Chapman (the maintainer of Dekko) is unavailable due to health issues... 😢 therefor any contribution to Dekko goes here https://gitlab.com/dekkan for now (since we can't merge them to master as long as Dan isn't around). Issues are still tracked in the original repo already posted by @advocatux: https://gitlab.com/dekkoproject/dekko/issues.
Also the webpage has gone down recently unfortunately... not sure if we will resurrect it, however we will continue to work on Dekko but progress will be much slower as long as Dan is unavailable. Up next: Dekko using qtwebengine to render mails instead of oxide - stay tuned.