I don't think this is good idea. mp_obj_get_int() means "get value of object when it is used in integer context", e.g. "arr = [1,2,3]; arr[True]". Following is not valid in Python:
~~~~
>>> arr = [1,2,3]
>>> arr["1"]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: list indices must be integers, not str
~~~~

So, function which converts string to int would rather have distinct name from mp_obj_get_type() and don't try to have much in common with it.