Wasn't "not wanting to release the engine yet" one of the reasons we didn't get offline mode until after launch? Now that we have offline mode, do we have access to the engine?
No, we do not have access to the engine. At the moment we have access to server scripts and can edit units/weapons/whatever, but that's our limit is how capable the engine is. You know all those requests We make to Uber for API's? If we has the engine we could make API's ourselves.
We can't write anything that directly interacts or alters components of the engine, if you define the engine as the binary blob. The server running locally is the engine, we can interact with it through the api. The api is enough to at least create the entire UI client side. It depends on your definition of "make our own games" as to whether we can or can not do so. Uber's tentative plan was to add features to the api as and when modders requested it. Something may happen in the future in that regard, however for the foreseeable future the focus will probably be elsewhere (my opinion).