First of all, the buffer will be too small for all tasks created on a branch and you don't want to have this buffer big, unless you have 2 monitors and have Emacs frame with this buffer opened for a half of it.
Also this process is not automatic - you have to navigate to the buffer and close the task when it's done. Also from the that buffer it's impossible to sync outside (GitLab/GitHub) or share your tasks with a team, what is possible with Kanboard if it's running on DigitalOcean/Heroku or simply synchronizes with GitHub.
If one really wanted to do it all in emacs' org-mode but also have it be automated and sycned with the code, I believe the solution would resemble something along the following lines:
Literate Programming in the Knuth sense with org-mode file using tangle[0] blocks holding the source code which can be used to generate and build the project, and a combination of regular emacs lisp code and some org-mode evaluated emacs lisp[1] to do whatever automation is needed.
Now the TODOs can be in the org file, which contains the source, and may also have a reference (automated) to the TODO, which when closed with the regular org-mode command (and is generally only two key chords) will remove the comment as well as update your agenda, calendar, kanban, etc.
Also this process is not automatic - you have to navigate to the buffer and close the task when it's done. Also from the that buffer it's impossible to sync outside (GitLab/GitHub) or share your tasks with a team, what is possible with Kanboard if it's running on DigitalOcean/Heroku or simply synchronizes with GitHub.