All my code which uses import probing would fail, such as fallbacks:

  try:
    import module
  except ImportError:
    import slow_module as module

Conditional support testing would also break, like having tests which only run if module2 is available:

  try:
    import module2
  except ImportError:
    def if_has_module2(f):
      return unittest.skip("module2 not available")(f)
  else:
    def if_has_module2(f):
      return f

  @if_has_module2
  class TestModule2Bindings(....

The proto-PEP also gives an example of using

  with suppress_warnings():
    import module3

where some global configuration changes only during import.

In general, "import this" and "import antigravity" - anything with import side-effects - would stop working.

Oh, and as the proto-PEP points out, changes to sys.path and others can cause problems because of the delay between time of lazy import and time of resolution.

Then there's code where you do a long computation then make use of a package which might not be present.

  import database  # remember to install!!
  import qcd_simulation

  universe = qcd_simulation.run(seconds = 30*24*60*60)
  database.save(universe)

All of these would be replaced with "import module; module.__name__" or something to force the import, or by an explicit use to __import__.