When someone sells hammers, they want you to hammer screws. Typemill is a document product and naturally, they want you to use that. It looks very polished and nice though, shame not packaged for distro though.
Typemill is open source with some paid plugins, I totally agree that a Markdown CMS is not the right solution, but it is an easy way to experiment with new workflows like this. I guess we will see other software in future if tasks will make the journey into the repos.
That's true, but it might also be the case that they think this is a good way to work and that's why they built the product in the first place. (I don't agree, though, I think tasks are more suited for DB storage).