I also recall him saying that he borrowed an idea from Russell T Davies, who already had a reason for why Frobisher looked like Lobus Caecilius. That reason was simply, that Frobisher was his descendent.
But what's also interesting is that he notes, ***SPOILERS FOR TORCHWOOD****Frobisher and his family dying was time's way of addressing balance for when the Doctor rescued the family from the fires of Pompei.
Perhaps his face is telling him that no matter what he does to change time, it will always balance itself out, and nothing he does can truly make a difference, which would be... dark.
There was also a big speech regarding Frobisher, that he was a good man who worked hard, even if he had to make bad decisions. I really hope we're not still hanging onto the whole "good man" theme anymore though >.> Its getting a tad tiresome.