I have .md and .org files in my content. The newly created content is .org
I tried the example given in the PR to create .md files.
For that I changed the type of some of my posts to cool. The newsletter which was created listed only the titles of the cool markdown files.
The cool Org files which I have tagged with +#TYPE: cool and I tried also +#TYPE: "cool" were not listed in the newsletter.
BTW: it would be nice to create also new Org content using the archetypes.