Ask yourselves this. If the line had one year left after they release the figures we've already seen (normal Goku, Krillin, 18, and Nappa), what would you want to see for those final figures? Let's say four.
Mine would be 17, Yamcha, Tien, and a Cell Junior. 17 because if I'm getting 18 I want to have 17 to go with her. Yamcha, Tien, and Cell Juniors because a sick 16 figure display could be made. Gohan fighting Cell, the rest of the Z-Fighters taking on the Juniors.
Yamcha and Tien would also lend themselves to Saiyan Saga displays with Scouter Vegeta and Nappa if you prefer. I'd give them alt parts so that they could be used for either saga.