The value proposition here is great...if you're living in 2016. But that framework ship has sailed. People already have years of experience deploying React (Native) targeting all those platforms and the web. Competition is great, but this new UI framework will join the same graveyard of all Microsoft's other similar attempts.
JavaScript will eat the world. At least Microsoft saved us somewhat by inventing TypeScript.
You can have JavaScript in MAUI. It's just as good a WebView host as anything else can be. I've seen plenty of "Blazor in MAUI" demos. (Maybe too many, as something of a sceptic about Blazor and its dumb brand name.)
MAUI is the "new brand on the street", but it's mostly just the latest revision of Xamarin's old stuff in a fancy new package and the option to call parts of itself in .NET now "System". There are people that already have years of experience deploying Xamarin stuff that (I hear) happily transitioned over to MAUI. (Sure, there's also plenty of people that think MAUI is too different from Xamarin and somehow killed their Xamarin puppy, because people will always hate any and all backwards compatibility breaks and semver MAJOR releases.)
JavaScript will eat the world. At least Microsoft saved us somewhat by inventing TypeScript.