I think author has good intentions, but I still suspect the real world is more complicated than expected; after all, in software development, the last 10% takes 50% of the time! So I have sneeking suspicion that it'll be hard to implement ALL Python 3 features (although Python is simple compared to C++, it's complex compared to compact languages such as Io or Lua).
I'd be more optimistic if he had a visible track record, although I give him credit for some realism ("close to C speed in tight loops with integers..." -- like I've said, standard Python can get close to C speed (e.g. matrix math in NumPy), if it spends most of its time calling optimized C routines).
SNAPpy is more like PyMite: only the VM in on chip (no interepreter, so not at all comparable to full Python, MicroPython, or eLua) and it's a very limited subset of Python -- the same nice syntax, but missing (IMHO, since I love lists, functional programming and metaprogramming) most of the good parts.
I don't know about this -- but I do know that the folks at Synapse Wireless use Python to create applications for their low-power wireless modules, and that they say their wireless stack, including the Python virtual machine, has a memory footprint of only ~40KB
This is a special version of python so you can't compare it to standard python. Author claims no need for external memory using the stm32f405.
By reading the technical details , the author seems to know what he is talking about, and he explains in detail including assembly code how can this achieve c like speed. Regarding real world usage, of course will have to see.
I'm very doubtful that MicroPython will be anywhere close to C speeds for real world applications. Regular Python isn't, although it can be fast enough, especially when used with other languages (e.g. NumPy, where most of the time is spent in optimnized C code or on my machine: Python is the flexible, top level; the real time stuff is done on dedicated DSPs programmed in C).
I'm also curious about size; if you use something like Py2exe, the result is typically in the multi-megabyte range. Maybe a SD card will be required...
eLua was started way before the mbed existed, and it does have a pretty wide reach (TI Stellaris & Tiva, Atmel AVR32 & SAM7, ST STM32, etc), so while it hasn't taken off like Arduino (what else has?), it's still alive and kicking, and has its place, as does the PicAxe, .NET MF chips, and such.