From its documentation [1] it looks a lot like a parceljs replacement [2], i.e. a zero config bundler which processes and bundles the dependencies in .html pages. So great for simple websites, not for replacing an entire Vite stack.
Thanks for the links! I should have researched a little more before replying.
It actually mentions HMR at the bottom of the docs, and I see plugins are already available. So while it can't currently replace my Vite stack for most projects, it seems like it eventually could.
I'm not sure how I feel about this sort of coupling in general, but for small projects it could be very convenient (as you mention).
[1] https://bun.sh/docs/bundler/fullstack
[2] https://parceljs.org