The dragonfires were part of the covenent, along with the Amulet of Kings, between Akatosh and the previous Dragonborn to help keep up the barriers between Oblivion and Mundus/Nirn. When Martin broke the amulet and became the avatar of Akatosh, he simultaneously broke that covenent and permanently sealed the barriers to Oblivion.
Being able to light the dragonfires now would mean nothing, unless a new pact was made that involved lighting the dragonfires.
There is no reason why another Amulet of Kings cant be made, or a new covenent renewed. I cant help but think of the Sword from LoTR that made reforged and given to Aragon. Similar thing?
The fact that the GI states that a Dragonborn can become emporer, and that you are a Dragonborn, seems to indicate that you will become emporer. I sure hope so.
I was a little dissapointed that of all the people that had helped with the Oblviion crises, who were the only one alive who had done so much, and in return you got little. Not even title of Emporer, that went to a pencil pusher who barely helped.