You could definitely argue that it would be better to build off of something like Contiki, a modern small-device OS that gained a lot of fame for its ports to old microcomputers, but is currently active in industry as well, with a new "Contiki-NG" version.
The appeal of Forth is mostly in a principled sense of, if you want Forth to be your interface, you have to build your own Forth, because Forth does as little as possible to structure you. And building your own Forth is not impractical; that's the whole point. It's wonderful as an exercise and can be productive in the right context.
But any highly developed or standardized Forth system gradually converges on being "just another platform." And once it's just another platform, it's an annoying dependency, and you end up demanding more structure for it to help tame the complexity, so the Forthiness habitually erodes.
The appeal of Forth is mostly in a principled sense of, if you want Forth to be your interface, you have to build your own Forth, because Forth does as little as possible to structure you. And building your own Forth is not impractical; that's the whole point. It's wonderful as an exercise and can be productive in the right context.
But any highly developed or standardized Forth system gradually converges on being "just another platform." And once it's just another platform, it's an annoying dependency, and you end up demanding more structure for it to help tame the complexity, so the Forthiness habitually erodes.