IF they decided that Titan class toys weren't only for G1 characters then Tidal Wave is the next logical choice, as well as a Supreme Cybertron Starscream and maybe a reimagined Cybertron Giant Planet Metroplex.

TaZZerath I like the idea of a Titan sized Ark with a robot mode (not Omega's robot mode but something similar).

Monstructor and Grandus are good G1 canditates. I could imagine them revisiting Combiner Wars teams at the size point like this as pseudo-MP toys - like the Constructions.

(I do not care for a Titan class Scorponok or Mega Zarak - that size doesn't fit how I see those characters.)