If you'd ever seen NYIF you'd know why it has to be kept away from anything that could damage the flimsy rubber sheath! I've seen rolls that were so badly mangled on the shelf in the store that I wouldn't buy them at any cost!
http://c.heimwerker.de/fa/_processed_/csm_stegleitung_detail_ef635d81a7.jpg1 mm2 is considered too small for fixed wiring in all European countries except the UK and Ireland as far as I know, on grounds of insufficient mechanical strength. In Austria it was banned soon after WWII if it was even legal after 1938 (introduction of the German regs. in occupied Austria).
I've never heard of up-sized earths being required, only suggestions that they might be a wise idea in some very specific applications. e.g. data centres.
Not having any exposed earth wire in boxes does make some sense to me and I assume that's the whole point of isolated earth conductors. The British require sleeving, which adds unnecessary labour costs, probably exceeding the manufacturing costs of fully isolated earth wires. Ireland started requiring full-sized isolated earth in 2013 and seems to have switched from T&E according to British Standard to NYM according to German DIN VDE.
