SDK - as always with our games, the tools to create maps and so much more! With Early Access, this will allow the creation of new levels. The full SDK support will be rolled out through the Early Access period.
Not sure when you took that screenshot, but thats what store page says right now. "Will be rolled out" ; what are those jews thinking?
There really isnt any reason to hide it from us; I take it they just f*ed up the steam stuff and its not showing up. The statement there implies there is still some kind of editor with initial release; even on the wiki page it says the beta version came with an editor.