Inspired by the thought of Captain John and Spike being the same person being:
Got stuck during a commute yesterday, and began to think about
this story, by
idontlikegravy where Spike is Captain John in a bit more detail. How could post soul Spike come to turn into the almost but not totally heartless Captain John Hart? What would bring him to the point where he would need to go to rehab for alcohol, drugs and murder. Why would he almost be at the point where he was when we first met him in the Buffy episode "School Hard"?
According to the story linked above:
It was the 51st century, he was Captain John Hart, renegade Time Agent, and he was completely and utterly alone. He got up and made himself a drink.
Completely and utterly alone? Angel dusted centuries ago? I would assume Buffy is gone, who else has Spike ever loved? Who else had Spike had a lasting connection to? Darla, who is long gone, and Drucilla. We know Spike dumped Dru for Buffy, but how would his feelings changed if she were the last surviving being with any connection to his past? The only thing left?
What would have happened to Dru by the 51st century? Dru is a lot like Lucy Saxon which brings up what I think is a very interesting question, what if Drucilla were to meet The Master? I'm thinking a young version Derek Jacobi's Master, long before any of the events of Utopia, perhaps even during the Time War?
What would be the nature of the relationship between these two characters? There is quite a bit in common between the two of them. Both have telepathic abilities, The Master because he is a Timelord, and Dru has had them since before she was turned. As we were told in "The Sound of Drums," the Master was driven insane as a child presumably after looking into the time vortex. Dru was driven insane by Angel before he turned her into a vampire.
How would Spike tie into all of this? Would losing Dru be the final straw that brings a rehabilitated, re-souled Spike back to his old ways? Perhaps that is what inspires him to begin to explore Whoniverse aspects of Time Travel. Maybe it is some of vengeance for things that were done to Dru and everyone else he ever loved? James Marsters said the difference between Spike and Captain John is that Spike was a Lover. What would make Spike lose part, but not all, of his ability to love?
As an aside, tying Buffy'verse vamps into the Whoniverse is a bit tricky. It would require taking into consideration certain aspects of the Classic Who episode
"State of Decay". So far, there are a number of differences between Whoniverse and Bufffy'verse vampirism, but if someone can create a paradox machine, I wouldn't put it past him change history by bringing vampires from another dimension back to the earth. The return of vampires could be attributed to effects of the Time War and the destruction of Gallifrey. If someone is going to be tampering with vamps and Spike in the future, also check out
Fray, a comic penned by Joss about a future vampire slayer. Part of its lore is that the 21st century is when demons get banished from the earth. Hmm...
In addition, in the Whoniverse, there are loads of alternate universes, perhaps the Cardiff Spike/John is visiting now is some kind of alternative, vampire free universe. Also, we don't see anything like Slayers in the Whoniverse.