This would be a huge deal for Python startup time *if* it was applied to all the standard library packages recursively. Right now importing asyncio brings in half the standard library through transitive imports.
$ time python -c '' # baseline
real 0m0.020s
user 0m0.015s
sys 0m0.005s
$ time python -c 'import sys; old = len(sys.modules); import asyncio; print(len(sys.modules) - old)'
104
real 0m0.076s
user 0m0.067s
sys 0m0.009s
For comparison, with the (seemingly optimized) Numpy included with my system:
$ time python -c 'import sys; old = len(sys.modules); import numpy; print(len(sys.modules) - old)'
185
real 0m0.124s
user 0m0.098s
sys 0m0.026s