I think that such a project would have multiple purposes: First off, you would take fewer things from Gecko, making for a more compact code base (I mean, does everyone want Video-in-Video and Pocket? Couldn't you integrate the most popular add-ons and remove add-on support? I like 'em, but don't they add bloat?). That could make the entry into development easier. Second off, it'd show people that Blink isn't the only engine you can base a browser off of. And if the code base is truly the same (includes Quantum), and more of a subset, it's probably easier to maintain and get security updates to than, for instance, Pale Moon. As fork developers are only able to backport security patches when Mozilla releases them, that problem would be greatly reduced if the project was made within Mozilla. Third off, having a lightweight browser might enable more people to use Mozilla products, as they could run the browser on weaker hardware. If the developers are able to focus on making that browser lightweight, it wouldn't be crucial for Firefox Standard to run on everything, and you'd still be able to reach more people.