It's possible since XWiki 10.10 to specify the type of WikiMacro parameters and since 11.5 to specify the type of WikiMacro content. However those types are only entered in a text input and are never checked until it's already too late (i.e. in the factory of the wikimacro). As a bonus getting suggest on java types would be great.
We should provide a dedicated picker for those java types.