Apparently Flashback are working on this. I got some form of newsletter from them yesterday that said the following:
"Final Fantasy VII For the NES Development Update
We have been working onn developing a new PCB to be able to run FInal Fantasy 7 for the NES. Initial Development is going well. we have tested a prototype and will be moving forward on this over the next few months. Hopefullly we will be able to offer this by this summer."