Graizen
has been asking for me to drop in on my opinion so I figured I would.
I have very little knowledge of digimon. If it matters the most I know is from Death battle, and the fact that digimon tamers was good and the digimon movie was not great. As such I am far from the most informed on the character.
Realistically Agumon is the digimon of choice. I feel his main competitor for a second Nanco is Heihatchi but he could work. My only concern is you would need to incorporate digivolving into his moveset, and that is tricky. Perhaps he is a charge character that digivolves into Greymon and warpdigivolves into WarGreymon and uses terra force as a final smash.
It could happen, but I feel you would need to make Greymon a clone of Agumon but much stronger for it to be feasible moveset wise.
Not likely in my eyes, but cool. A solid 20% Chance from me when we do him on RTC someday.