It's going to be an extremely simple browser. Their strategy is to use the HTML rendering component built into each OS. The way I interpreted it was that they're trying to make a browser that's simple enough to develop with a small team, "good enough" for most people, and doesn't have every feature under the kitchen sink.
> Will this be open source?
Doubtful. It also doesn't "make sense" to open source, as they're basically using the same rendering engine as Edge / Safari, with a different UI around it.
(Side note: If you want something like this that's open source, it's probably easier to clone it than to fork it. Every few years I write an experimental browser based on these rendering engines, and I frequently come across "simple" open-source browsers that provide great examples of how to use these components.)
> Will this support WebExtensions?
No. They are building ad-blocking and privacy functionality into the browser. To paraphrase what they told me, most people only install ad-blocking and privacy extensions.
> Will this allow ad-blocking and tracking protection?
Yes, that is the major feature they are trying to build. They have extensive blacklists already, as they already ship privacy-focused plugins for Chrome. (Their take-home assessment involved using a well-known privacy list published on Github.)
> Will this allow usage of other search engines within the browser, or are you locked in to DDG only?
We didn't discuss that. This is speculation on my part, but I think their motivations are to "keep it simple" instead of offer every feature under the sun.