The major theory behind it is it allows for printing of infinitely long parts. The way this would work is essentially treating the belt as a 'sliding window'. I would assume they've written a slicer which is able to utilize the belt and print certain areas of the print before others, in a 'sliding window' fashion. Very cool. Much more interesting than mass-production, which as the post I just deleted pointed out, I see much less use for with FDM.

An image from the article demonstrates well:

Now, I could see the part sagging due to gravity. That would likely have some consequences, especially at printing temperatures. Regardless, this is an awesome implementation.

Based on the article if you read it, it uses all the standard types of filament. There is a heater under the belt to keep the print area the required temp for ABS.