James Marsters is open to the idea of returning as Spike for the new Buffy the Vampire Slayer series. Marsters, who currently plays Victor Stein on Hulu's Runaways, was a huge part of the original TV series, first appearing in season 2 as one of the season's main villains, Spike. After appearing intermittently in season 3, Marsters was added to the cast as a series regular in season 4 and stayed with Buffy until the final episode.
As an undead vampire (with a soul), there are some obvious visual complications to Marsters reviving his role as Spike. Vampires don't age, and James Marsters doesn't look exactly like he did in 2003 when Buffy went off the air. Yet Marsters is willing and confident that the Buffy reboot could make his return as Spike work.
James Marsters was asked about the new teen horror series and if he's interested in joining it in a group interview with reporters on the set of Runaways season 2 (via /Film). The actor was very enthusiastic about the possibility, answering:
"I am open to whatever Joss [Whedon] has in mind. Whether that’s playing Spike or something else, I told him a long time ago. Joss’s mind is always surprising so I’m open to playing Spike if Joss is involved. I think we’d have to get some really good lighting together to sell Spike, but they are doing more and more and more, both with actor health and with special effects. What would be great is if he comes back and he’s like, ‘Buffy, you look terrible. I still love you of course.’ That would be fun."
The new Buffy the Vampire Slayer is still in the early stages of development. All that is really known is that the original series creator Joss Whedon is producing, the (potential) series will be run by writer Monica Owusu-Breen, and it'll feature a black lead. Interestingly, Owusu-Breen recently suggested that the Buffy series will be more revival than reboot. While, none of the original characters will be replaced, it is time for a "new slayer." A new vampire slayer would work in the context of the Buffy universe. The series finale ended with Buffy sharing her superpowers with every girl across the world who could become a slayer and starting her own private army of powered teenage girls. It wouldn't be too hard for the new series to pick up that thread a couple decades down the line.
If the new series does turn out to be a sequel, it would be rather odd if Spike wasn't featured or at least mentioned. Although he started the series as a villain, Spike eventually become a strong ally of Buffy. Spike even fell in love with her and their twisted romance was a huge driving force of the final two seasons. It still would be difficult for a technical standpoint to bring Spike back. Cinema has made great strides in de-aging actors and characters, yet the technology is nowhere near a feasible level for a TV budget, especially on an ongoing basis. Marsters could appear as Spike as a cameo and it wouldn't be too noticeable. However anything longer than a quick scene would get very distracting, very fast. The better option is probably the one that Marsters throws out casually; he could return to the world of Buffy as an entirely new character. The character's resemblance to Spike would have to be explained or at least mentioned, but that's nothing a quick joke or some crazy supernatural exposition couldn't fix.