reserve a TLD, like ".v6", and you are done. URL parsers don't break, the amount of code to change is not that big, and many of the user-space applications can

reserve a TLD, like ".v6", and you are done. URL parsers don't break, the amount of code to change is not that big, and many of the user-space applications can keep working with no changes at all, as long as they use high-level network libraries. If you really hate this for some reason, use some other characters. How about underscores (_) for example? Those are not valid in DNS, so there is no chance of confusion. Choosing colon when URLs were already using it is either very stupid or very mean.