The proposal makes sense at first glance, but I agree with Mark that it is
not clear what should be done. For example, all arrays in Python silently
convert to inf:

>>> from numpy import array
>>> x = array([1,2,3], 'f')
>>> x
array([ 1.,  2.,  3.], dtype=float32)
>>> x[0] = 10**100 
>>> x
array([ inf,   2.,   3.], dtype=float32)


Same for array.array and memoryview. I would not be surprised if users rely
on this behavior. Anyway, silently converting to infinity is exactly what
I'd expect (also for double BTW).

 
Regarding undefined behavior: I only know compilers that convert to infinity
without signaling overflow. The tests for the new memoryview implementation 
should include this case (I think!), and I ran the tests with all compilers 
that I've access to.