And this is exactly what has made Python in embedded systems possible. There is no way Python would ever be practical on an ATmega328P but on an STM32, ESP8266, ATSAMD21, etc. board you have plenty of memory and clock cycles to fit a reasonable sized project and an interpreter even if the code is not as efficient as it could be.
This is exactly the kind of dicussion I wanted to start with my post ...
The reasoning is going to be philosophical rather than a technical/economical one (in this arena I'd agree with you 99% of your post): The main question is: Is the arduino project addressed only to developpers?. (Look that I've said "project", not "forum").
Sure we would have to ask Benzi, Cuartielles & Co to make sure, but I can still remenber the first notice I had on arduino: Benzi striving to teach the viewer (it was a youtube video) how to switch on a LED by means of a switch both connected to an arduino UNO. Not much on an embedded systems; even more, there's a long, long way beetwen a LED, a switch and an embedded device.
For a hobbyist, spending an extra $1 for a microcontroller with the extra capacity to allow for an easier programming experience is no big deal. For a mass manufactured product it will be worth paying the salaries of the programmers for the extra time to write efficient code that can fit on a slightly cheaper microcontroller.
This is a different issue: is "spending an extra $1 for a microcontroller with the extra capacity to allow for an easier programming experience" "not a big deal". I'm not sure if saying "1$" means exactly 1$ (I'm spaniard), but the fact is that, in many cases it is just a "1$" -or less- deal. Do you think that such a small quantity(es) pays a hobbyst the effort of learning "C++" instead of using python?; I'm not sure on this neither.
So to me it seems like Python is good for a hobbyist but will rarely be the choice for a professional embedded systems programmer. Is it really worth it for a professional to learn an additional language just for the rare cases where Python does make sense to use? The thing I really like about Arduino is that, even though it's meant for beginners and hobbyists, the knowledge gained could be applied directly to a professional career if that's where it takes you. If you get started with Python and then decide to embark on a career in embedded systems programming all your Python programming skills you learned will not be used and you're going to need to learn C/C++ instead.
I'm back on the first paragraph: who said that arduino is just a (such a) professional bussines (arduino, I insist). Even more: who said that using a M0 with python is not reasonable for certain projects?. What if I just want to make a few units of a greenhouse monitoring (two or three temperatures and soil moisture sensors; a couple of relays) system for some of my friends?. Should I allways use a vintage road bike (with those awfull gears) to climb the Tourmalet or may I use a mountain bike to do the same?