It looks like they are releasing these bits and pieces before the Finale. Custom ARM core, SOC in entirety.
Googles ad revenue is so important that they should do absolutely anything and everything to protect it, spending billions on R&D to keep android at the forefront is essential, and at the moment they are only really competitive on the software side (A11 smokes latest snapdragon chips, as does the A10....), offering a custom chip would give android the vertical integration that Apple leverage to be so dominant.