I prefer C#/F# over Dart, but Flutter is promising, and I continue to check in once and a while. I usually overcome PL preferences when the platform or toolkit is compelling. I remember Notch (of Minecraft fame) adopted Dart very early on, and I actually tried it out back then. Somebody had written a Lisp in Dart. I really like F#, and it seems to be sidelined all the time with .NET. There are more and more ways to write C# in a functional way, and it has become the lingua franca of many game engine/3D media creation tools like Unity, Wave Engine, Flax, and Stride to name a few.
I'm not sure what your bar is for "experimental", but Flutter is one of the most popular UI toolkits out there, with many 100m+ MAU apps using it, including tens from Google itself. It's already shipped a 2.0 release, has 15,000+ packages on the pub.dev package server, is the framework Ubuntu has settled on for new desktop apps, has hundreds of active contributors, and is one of the top ten OSS projects on GitHub.
"Experimental" feels like an odd word choice, if you're truly trying to offer useful information.
A lot of devs are risk adverse when choosing platforms for projects. There's still risk as in, will this still be supported in 3-5 years and is the API going to change so much in 1-2 years I'll be rewriting significant portions of my application.
I've been passively looking at Flutter with interrest.
Also, the Dart lang team seems to consider Flutter a first class citizen and has been modifing the language for it specifically. From syntactical sugar for Flutter's constructors to carefully selecting language features considering muilti-target platform performance.
It really is the project to beat. I am not sure how you are gonna drop a framework over C# and compete with a framework/lang combo long term.
Some people think like this: if i write an app and come back in 10 years, is it still going to work, compile, and be possible to update? By that benchmark very few platforms are acceptable, and they are mostly first party.
That standard makes sence if you have a rigid hardware-like approach
Yeah, that makes a lot of sense for certain platforms. I've spent a lot of my career working with enterprise customers, some of whom are comfortably running 20 year old software written with something like WPF. And in general, that would be true of Flutter too -- on a platform like Windows, it will work at least as long as the underlying Win32 APIs are available.
(Of course, that's not a viable test for most mobile frameworks. I suspect that an iOS Xcode project from 2011 would not run without rework, nor an app written for Android Honeycomb.)
Flutter is open source, which provides some automatic measure of protection against obsolescence. And companies like Toyota who are building it into embedded systems like cars that will still be around in 20+ years.