I've just read all the way to the most recent manga chapter which is chapter 466 of fairy tail and Natsu has just used, and seemingly lost, the Dragon King Mode. It seems that all hope is lost for the fairy tail mages since natsu has now depleted the Dragon King mode and the guild has lost their trump card to defeat zeref.
Here is my question. Can Natsu theoretically combine the Dragon Force with his lightning flame dragon mode in sort of a stacking kind of way? From what I understand about Dragon Force it is the most powerful transformation that a dragon slayer can take and puts their overall power on par with an actual dragon. It increases their strength, speed, power, senses and their overall magic power to unimaginable heights. Now from what I know about Lightning Flame Dragon Mode it increases the strength of natsu's attacks as well as grants him the ability to use Laxus' lightning to increase the power of his magic related attacks.
Here's the thing, it seems to me that Dragonforce is a full on transformation that can be utilized by the dragon slayers but it seems as though Lightning Flame Dragon Mode is more a power up that Natsu can use to finish a fight quickly rather than being a full on transformation. So it seems that it would only be logical that Natsu would be able to enter Dragonforce and then power up utilizing LFDM to end a fight with zeref quickly. If he could utilize both would this put him on par with the Dragon King Mode and would it be enough to defeat zeref who was almost critically wounded by the Dragon King mode?