Hi!
I've been using the http://wikidata.org/ontology# namespace for datatype properties for some time (more than a year). Now I can see everywhere only the http://wikiba.se/ontology# ns. Was there some reason for change? Are these two somehow compatible? Will the first one be deprecated?
The items in wikiba.se/ontology hierarchy are those that would be relevant and would have the same meaning for any Wikibase install - i.e. individual statements, ranks, properties, etc., basic data type predicates. They do not depend on particular Wikibase instance, thus they were moved to wikiba.se. If you have your own Wikibase install, your items and properties would carry your domain name, since they are not Wikidata items. But Wikibase ontology would stay the same. Thus the difference.
And yes, the old form of the ontology URLs will not be used anymore on Wikidata or Wikibase code.