I've read the whole thread, and I wanted to repeat a critical point for emphasis:
This doesn't help
No matter what you do to improve conversion issues, you're still dealing with the underlying floating-point problems, and having watched the changing discussions in c.l.py since we moved to the different conversion system, it seems clear to me that we've improved the nature of the discussion by forcing people to get bitten earlier.
On the other hand, it is pragmatically more convenient when an implementation prints the values of floating-point literals with a small number of significant digits with the same number of significant digits with which they were entered. If I can enter a number as 0.1, printing that number as 0.1 does not introduce any errors that were not already there, as proved by the fact that reading that 0.1 back will yield exactly the same value.