Something is happening on apexea.oracle.com. It looks like the APEX team is preparing the first 5.1 early adopter release. At the moment you can see only a coming soon page. However yesterday I visited the page and for a couple of minutes I was able to see these screens:
This is definitely not a final announcement and as you can see, some things are still in work. But it gives us an idea about which features are going to be included – either in 5.1 or later.
