They are dummies / spacers, just blocks, no way to enable them, theres nothing in them, they are put there to stop the IHS from bowing under pressure from just having 2 cores under such a large package.
http://www.pcworld.com/article/3211...en-threadripper-has-two-mysterious-chips.html
But this from AMD along with Infinity Fabric opens the door upto much wider possibilities, they could quite easily remove those spacers, and stick an extra 8/16 die in there, very quickly and easily you suddenly have a 24/48 CPU or remove both spacers and you have an 32/64 CPU, and with them moving to 7nm next year, thats a die shrink, they could get even more under there if they can keep the TDP down, Intel are rushing out a whole new bunch of useless toasters at the moment, just take a look at the 7800X with X299, AMD's 1600 matches its speeds for more than half the price.
In 2018 when AMD start working on their Navi GPUs, as far as im aware, there intentions are to use infinity fabric with those too, like multiple die's onto one package to create a very fast GPU.
This is a bit long winded, but its a great watch explaining what the possibilities are for AMD with Infinity Fabric: