Replicant

Context: https://hackaday.com/2013/08/02/sprite_tm-ohm2013-talk-hacking-hard-drive-controller-chips/

So the charging board died on my Galaxy s2 some weeks ago. I purhchased a replacement which was lost during shipping for two weeks and then was 'found' and delivered to me.

My question is, assuming someone had physical access to the board and could reflash the firmware, to what extent could the i9100 as a device be compromised?