Really, the Tao Trio only really needs one more forme change, and that's the Original Dragon, AKA Kyurem fused with both Reshiram and Zekrom. They're a good way there, as Black/White Kyurem are only missing the opposite Dragon from the Tao Trio, but I really can only see the most fitting ultimate forme for the Tao Trio being the Original Dragon, after all they were all the same Pokemon at a time. Prehaps keep Kyurem's Ice/Dragon type and give it a Ability that gives it Pseudo-Fire and Electric STAB, but I'm getting off topic here.
I completely agree, but what if instead of combining all 3 dragons we just used the dna splicers to combine reshiram and zekrom? i mean they are the two halfs of the whole. what would be interesting is the movepool and typing, maybe a new dragon move like "origin blast" or something like that, and give it access to all three of the dragons movepools with a dragon/? typing. Ability and the second type are the only things i cant figure out