This would be more of a "scripting" Forth vs a full bottom up programming language. It would expect to be embedded in C and able to call C functions (like a scripting language!).
Right now I have something working on both a PC and MSP430 (simulator). u4th is written in C and makes no presumption about I/O (you can extend and add UART support, but it is happy to just work with a dictionary and an init() function). It supports a RAM or ROM/Flash resident dictionary (but no Flash writing support built in). It compiles a position independent dictionary that can be transfered to/from a PC and MCU without modification.
It does not implement ANSI Forth.. it is it's own beast geared for scripting, not system building.
I have a few more things to add (no DO .. LOOP yet) , but right now it runs (interpreter + VM) just under 4KB RAM (with a 2KB RAM resident dictionary -- so if the dictionary is Flash based, we are talking well under 2KB RAM!) and around 7KB of program (flash resident code).
More to follow!