After the old trio back, my wish would be to see again Genra and Raidou.
Also if I like Akira, Sarah and Pai no more VF character for me in Doa5 - I would prefer to see them in an eventual future crossover of the series - if we need of another guest I would be glad to play with Ryo Hazuki or Spartan 458/Nicole (also if this is impossible considering the exclusivity of the Halo franchise).
Shiden for me it was really interesting: a sort of Doa3 Hayate, considering the big difference in his DoA4 counterpart, anyway in DoA5 would be needed to make him much more different from his son; for the same reasons was nice to play with Doa2's Kasumi in her clone, but also in this case I would prefer an evolution of Kasumi alpha gameplay.
Impossible final wish: the inclusion in the roster of Sonia/Irene
Anyway I'm sure that we will see Ein and Tengu together with Leon and Momiji, but not so much of other characters (anyway I hope always to be wrong XD)