Quite frankly OSPi is very confusing. I don’t blame you or anyone for any confusion regarding any of the software. With that said, the May 4 announcement here is NOT regarding the new UI based python interval program. It is for the master branch of the OSPi software using the OLD UI. Furthermore, all changes related to the plugin system are happening on the master branch not the JM_UI branch.
The thread you linked by the way says beta in the post and is followed with many posts regarding issues with the branch. Again, I think it is being developed out still and would stick to the master branch for reliability purposes.