That cloud (the one I linked to) contains ALL TAGS for ALL CONTENT TYPES (not just Showcase). The OLD Legacy system (which was a stand alone tags system for showcase only) had tag cloud functionality built into it. All of that programming code has been removed and would not work with the new tags system anyways. I've not yet seen any addon (RM, XFMG included) that has a Content Type specific "cloud" developed yet (and I don't think the core Tags handler has code to produce one). It is something that would have to be developed.
I can move this to suggestions, however, I am not sure I am going to develop one when I am sure that Core XF will eventually have something that addons can use.