If you have a very large project which uses MobX, I don't think the amount of warning matters. You'll most likely have to (eventually) completely rewrite large amount of code, to the point where it might be easier to migrate to SolidJS.
If you have a large project then it's your victory or fault for whatever comes of using software marked as not ready. The React team has been absolutely clear that it's not ready.
On an aside, SolidJS has been taking a huge momentum hit recently, I think the drop in downloads is a lagging indicator. It's not an easy space, I love SolidJS and recognize that Ryan Carniato likely took a career hit to work on Solid, but my bet is that Solid will fail to catch critical mass. Really sad as I love the Solid experience.
