I am sure that Ford has both engineers and beancounters on the "V8 for the Raptor" case but the biggest determinant for the V8 Raptor will, without a doubt, be that Ram 1500 Rebel TRX. If that thing starts eating into Raptor sales significantly, I think we will see a return of the V8. That said, I don't think that TRX is due until 2021 so we are probably looking at the 3rd generation Raptor at that point I would assume. I really do not think that Ford will put a V8 into this Raptor.
Ram is already gaining massive amounts of market share, mostly at the expense of the Silverado, so they have tasted blood and would probably love to own the lucrative full-size off roady segment as well. Their Power Wagon is simply positioned differently and, as executed, represents no threat to the Ford. If I were running Ford, I would be scrambling to get ahead of the curve and would be preparing a V8 Raptor to debut prior to the TRX launch to steal some of its thunder. If that TRX bases below $70K, it is going to eat the Ford's lunch. They are already talking about two versions: a full fat version with all 700+ Hellcat horsepowers and a "lite" version with more like 500ish. That lite version, priced in the mid-$60K range should terrify Ford execs.