Design time and Runtime for ADF Swing is still there in JDeveloper 12c to support existing customers.
However, we are not actively developing this technology since the 2011 announcement of its deprecation.
If you are looking to build new mobile or browser based applications, you should look at the latest versions of ADF.
If building new client applications with Swing is what you're interested in, we continue so support generic Swing development.
We've improved Swing development in JDeveloper 12c, by incorporating the Matisse Swing editor.