Mostly fixed by PR 16545 (see issue13153). The original example is now passed.

>>> raise Exception('\U0001f603')
Traceback (most recent call last):
  File "<pyshell#1>", line 1, in <module>
    raise Exception('\U0001f603')
Exception: 😃
>>> 

But you can still cause a restart of the shell by using surrogate characters:

>>> raise Exception('\ud800')
Traceback (most recent call last):
  File "<pyshell#0>", line 1, in <module>
    raise Exception('\ud800')
Traceback (most recent call last):
  File "<pyshell#0>", line 1, in <module>
    raise Exception('\ud800')

================================ RESTART: Shell ================================
>>>