And I think it's fair for someone to put together a proof of concept as a research proposal. They may not make it far in and of itself, but it may become an inspiration for someone else.
GUI crate maintainers have expressed interest in AccessKit; so far three crates have started using it (egui, rui, iced in a PR).
This suggests to me that these maintainers are interested in the idea of pooling work and that they're willing to use other people's work instead of NIH-ing their own library. (Though that doesn't mean Masonry is what anybody will settle on.)
The "potentially never stable" part is fair to worry about, but I disagree with the "start a new one" part.
While I do want to work on another UI library (Panoramix), this isn't what this post announces. The goal of Masonry is to promote code reuse. In my ideal scenarios, other libraries such as Xilem, Iced, SlintUI, etc... might come to rely on Masonry as their backend.
In fact, the "xkcd 927" problem is why I started Masonry in the first place: because I saw there were a lot of Rust GUI frameworks, but there was no crate that gave you a base to build a GUI framework from.