The people who use the phrase "sane subset" are those who in my experience distort C++ beyond recognition by banning particular features of the language wholesa

The people who use the phrase "sane subset" are those who in my experience distort C++ beyond recognition by banning particular features of the language wholesale rather than shaping the programs that they write to fit the environment. You should be using the whole C++ language. There's no such thing as a "sane subset", because all of the language has "sane" uses. What you want is to create good programs.