> I'm not sure how likely Mozilla is to develop it into a product

It's unlikely to become a standard desktop browser, but the roadmap [1] does mention investigating options like a standalone mobile browser [2] or perhaps to be used embedded in an app, e.g. for packaged web apps.

[1] https://github.com/servo/servo/wiki/Roadmap [2] https://github.com/servo/servo/issues/20855