October 2019, Serhiy solved the display issue with a _tkinter patch for #13153.
bpo-13153: Use OS native encoding for converting between Python and Tcl. (GH-16545)
https://github.com/python/cpython/commit/06cb94bc8419b9a24df6b0d724fcd8e40c6971d6
In Windows IDLE Shell
>>> ''.join(map(chr, [76, 246, 119, 105, 115, 0x1F40D]))
'Löwis🐍'
except that the snake is black and white.  (Many astral chars have no glyph and appear as a box.) In console REPL, the snake shows as box box space box.

Pasting astral characters into edited code 'works' except that editing following code is messy because the astral char is multiple chars internally and the visible cursor no longer matches the internal index.  (But pasting such no longer crashes IDLE.)