It wasn't obvious from the article, but the printer also supports 11" wide paper rolls for us American users.
Honestly, beyond just the openness, the small form factor also looks really compelling.
Tabloid printing used to be quite inexpensive... Any 11" wide dot-matrix printer could manage it.
The rise of inkjets made it relatively more expensive. I resorted to rescaling tabloid (11x14") printouts to US Legal (8.5x14") to keep old business applications working.
In recent years, as A3 format copiers (with network printing) have become very common in offices everywhere, it's becoming inexpensive to print on tabloid sized paper once again.
Edit: The project description does indeed state 27mm as one of the supported formats (A4 and A3 width are also supported). Seems an odd choice to me, but there may be a market there I don't know about.
Or perhaps they meant 297mm - the exact height of a sheet of A4 - and mistyped the "9".
90% of what I use my printer for is printing mailing labels for packages.