'Colon' denotes point of view in ordinary English usage, as in dialogue. All chat developers know this. mediawiki knows this. But somehow the period is going to be overloaded yet again to create namespaces ? When the primary use of namespaces is to differentiate a POV, i.e. that of the service, or that of an individual user, or another meta-perspective, from the main namespace?
Colons in URLs certainly tell the browser which protocol it's going to speak. Likewise, the rules of handling content will vary drastically based on which namespace it's in. There's a natural convergence between the use of colons in URLs and the use of colons in English, which mediawiki respects. Creole should too.