Till the end, I was holding out for Gary Mitchell to be the villain of STID.
I doubt they would have used an adaption of Where No Man Has Gone Before to star the NuTrek ongoing comic if they were planning on using Mitchell considering that the NuTrek novels that were cancelled seemed to touch on stuff that was in Into Darkness.
Not to mention the fact that for "Harrison" to be Gary Mitchell would have required nerfing Mitchell considerably considering he had godlike powers.
It also doesn't work for "Harrison" to be Soran either because he never had super human abilities near as I can tell.
Also no offense but destroying the Enterprise-D doesn't make someone a threat since the writers made that so easy a kindergartner could do it.