Thought I'd give it a try. I installed Oracle 12c with a container DB and one PDB. The basic database install comes with 4.2.0 and after a day or two fiddling with it, I managed to get it to work with an embedded pl/sql gateway. The tricky part was getting the pdb to interact with the apex installation in de cdb. Then I applied the latest patch to get the version to 4.2.2, and everything went to hell in a handbasket. When executing the apxchpwd script I keep running into an error (ORA-04023: Object APEX_040200.WWV_FLOW_UTILITIES could not be validated or authorized), which I just cannot appear to solve. Somehow it also killed my (cdb) EM Express access on port 5500, as that no longer works either. I ended up deleting the plugin DB completely and recreating it using the dbca, but the error just comes back. I now want to uninstall Apex completely from the cdb as well, using the instructions I found here: Utilizing the Multitenant Architecture, but there a reference is made to a patch (16946990), that I do not find on the support site. So unless anyone here has any suggestions on how to continue, I'm throwing in the towel and sticking to Apex on Oracle 11g2. I will give 12c a try again when it matures some more, in my experience that means waiting for 12.2 ;-)
I recommend reviewing my colleague, Jason Straub's blog on this topic: Application Express Nuggets: Oracle Database 12c Multitenant Option and Application Express, where Jason explains that our latest patch release, APEX 4.2.2, does not contain the patch installation files for a 12c container database, because 4.2.2 was released prior to 12c:
...we have not released a new version of Application Express since Oracle Database 12c was released two days ago, so there is no software available to upgrade or patch the version of Application Express (4.2) that comes in the container database. The next version or patch of Application Express will contain the appropriate scripts to update a container database...
So until the next APEX release is made available, you would need to stick with the version that comes with 12c, which is currently APEX 4.2. I hope this helps to clarify things.
I just wanted to inform you that we now have a revised APEX 4.2.2 OTN distribution available, which contains the necessary scripts to install APEX 4.2.2 in a container database. Jason has blogged about this new distribution, here, and has also outlined the necessary steps to follow in order to install 4.2.2 in a container database. Please note that this does not cover the patching of a container database from 4.2.0 to 4.2.2, but instead covers the removal of 4.2.0 from the container database, and then the fresh install of 4.2.2 in the container database. Hopefully this will help you to get the result you were hoping for - to have 4.2.2 running on your 12c database.
As mentioned in my previous post, if you wish to patch 4.2 in your container database to 4.2.2, you'll have to wait til our next release, as it will contain the necessary patch scripts for that upgrade effort.
There is also now a brand new page on the Application Express OTN page all about APEX + 12c. Click the Collateral button and then the Application Express in Oracle Database 12c link.