Forth is very cool and I agree with what you said, but it is arguable how useful it can be although OP didn't specify that he cared about that (he hinted at what would be a better replacement). I think there are a lot of things you'd have to implement from scratch or attempt to find a collection of words for, which might not work on your Forth. So if you're Chuck Moore then you're good. If not, I'm not sure if the extreme advantages (tiny size, REPL, ~speed, high ceiling/low floor) make up for the fact that you're essentially working in a vacuum.
You can squeeze a FORTH kernel into 2K, so 8K really is quite a luxurious size. I actually wrote FORTH code very early in my career and wrote lots of things you might not imagine doing. For example I wrote a 3D star field animation system for a planetarium in FORTH in the late 80's.
I think programmers (especially these days) over estimate how much advantage they get from reusing other packages. Because it becomes so much more difficult to refactor your code when you can't change some interfaces, you may end up with more (or at least more complicated) code than if you wrote something that is tailor made. In languages where you have a lot of facilities available, it is one of the hardest decisions to get right. When you are forced to write everything yourself, then it's easier to get the choice right ;-)
