So there are a few reasons I'm personally interested in it:
It isn't being created as the "heart" of a browser - i.e. it is a project to develop the engine and not to develop a browser
Supported by the Linux Foundation rather than any of the tech corps like Facebook or Google
Written in Rust - I'm not claiming that this is good because of the language technology itself but Rust is currently very popular with lots of people wanting to learn it and contribute to projects so hopefully this inspires people to get involved with it.
Not a KHTML/WebKit/Blink (or even a Gecko) fork
Repo is on GitHub - Don't get me wrong, I'm not a GitHub shill, but generally people monitor and know how to use GitHub better than Google and Mozilla's systems. I'd honestly be just as happy if using GitLab or any other alternatives as they still confirm to that same user experience (and to be fair WebKit is also on GitHub).
And none of those touch on the technology itself which, honestly, I'm not experienced enough to speak on why it is as good as/better/worse than KHTML/WebKit/Blink or Gecko. Words and phrases like "memory safety", "parallelizing" and "performance" are thrown around but I'll leave that to the judgement of those who know better. You might like to have a look at some of the links in https://github.com/servo/servo/wiki/Browser-Engine-Research if you are interested in that front.
From what I understand, Gecko was a terrible engine from the get-go. It is also difficult to work with, and had a lot of idiosyncrasies that made hard to build anything that isn't just a clone of Firefox. There's a reason why Apple used KHTML as the basis of Safari and not Gecko. Even Brave is based off of Chromium, and the founder of Brave is one of Mozilla's founders!
So apparently no, Gecko is not it. We need something closer to a pure browser engine that is open source.
Which means they don't fucking understand how browsers work.
Anyone can make a new fork of chromium, Vivaldi has created their own ad and tracker blocking that doesn't rely on Google or the manifest v3 change that broke ad blocking on chromium for everyone else.
You don't have to rely on Google for shit if you're committed to making the fork your own.
If that's your metaphore, then the browser engine is the kernel. Have you ever seen a Linux distro forking the kernel and taking it into a different direction? It's always just (relatively) minor changes, if any, so that keeping up with the upstream kernel is possible. Mostly a matter of built-in drivers, and a security feature here and there.