Yami Bakura was a great villain. One of the best in the Yu-gi-oh world (Second to Yami Marik for me XD) but again what purpose would he have? Attack a duelist school? Sounds like a major downgrade from taking on the Pharaoh in ancient Egypt with living God Cards, Exodia, and Zork clashing. I'm very glad none of the old cast were regulars on Gx. Cameos and references are always welcome and even small crossovers like the 5d's movie are welcome, but for them to appear back to back is to much and it cripples the young blood of the new cast. I'm just a guy who loves change. I love getting fresh new starts while at the same time respecting the old.
Maybe Bakura's spirit could've been after a certain student who would have been the key to his revival or something. I don't know, but the writers could've easily come up with something if they had wanted to. I guess it's good that few of the older characters appeared in the GX series. They had their time in the original series, after all. I haven't watched 5Ds much, but were there any cameos by older characters in that series? Apart from the movie, I mean.