James Marsters, the actor who portrayed Spike in Buffy the Vampire Slayer and Angel, said he would return for a reunion if Spike only appeared in vampire form. Buffy, created by Joss Whedon, was a wildly popular 90s television show about the titular vampire slayer and her trials and tribulations throughout her life. A unique part of the show's vampire lore came with the fact that vampires had two forms: one that looked human, and a "true vampire" form where their fangs would come out, their eyes would turn yellow, and their brows would scrunch.
Marsters joined Buffy during season two, taking on the role of the vicious, yet endearing, Spike. Marster's character was intended to be a short-lived villain, and the original plan would have had Spike die during season 2. However, Spike ended up being immensely popular among the fan base. The character ended up having some dramatic shifts, morphing from a villain to something more like an anti-hero. Spike's tenure in the Buffyverse didn't stop with the show's end, as Marsters went on to become a main character during the final season of Angel. If there were ever to be a Buffy reunion, Spike's return would be paramount.
During an interview with Michael Rosenbaum on his podcast Inside of You, Marsters said that he would only come back for some type of reunion if Spike stayed in vampire form. The actor mentioned that he thought he was too old to play Spike now (it has been 16 years since Angel ended), and that portraying an aged vampire would go against one of the core foundations the show had set up about the creatures. Marsters said he was more than willing to come back for a reunion, but under the condition that there would be some way to hide the age difference. One of the solutions he posed was that Spike would only appear in vampire form. Marsters said:
"Yeah... I told Joss during Angel that if he called me for anything, whether it's one line or 50, I'd come, no matter where I was in the world, but if he wanted to film me doing Spike he had seven years. Because I'm aging and Spike's a vampire, and I don't want to play an aged Spike... If there was a way, or if Spike was always in vampire face. Then that might work."
The idea of a Buffy reunion has been floating around the air for quite some time, particularly picking up steam around 2017 when the Buffy cast reunited for Entertainment Weekly. The fact that Marsters is being asked about it shouldn't come as a surprise. We're right in the middle of an age of reunions, with shows like Friends, 30 Rock, and Parks and Recreation, all receiving reunion shows sometime in 2020. There would certainly be an audience for a reunion, especially considering a popular Buffy comic continuation runs to this day.
There are several ways to get around the "vampires don't age" problem. Digital de-aging technology is becoming more and more popular, although it has its own drawbacks when it comes to the cost and the potential of creating an unsettling "uncanny valley" effect. There is also an in-universe solution. In the Buffyverse, certain vampires, if they were old enough, eventually took on a permanent "vampire face" form. It's possible that Spike could have reached that point whenever the reunion would be set, giving Marsters an inherent reason to always be in makeup.
However, there is also a good chance that Marsters' concerns wouldn't be shared by the fan base. There seem to be a plethora of ways the creatives behind the show could come up with to justify the vampire's visible aging, and it probably wouldn't take much to fall within fans' suspension of disbelief. Nearly ten years passed between the beginning of Buffy and the end of Angel. While not dramatically, all the characters (including the vampires) did age on screen during that time. It never seemed to be an issue back then, and if fans were given the chance to see more live-action Buffy the Vampire Slayer, it most likely wouldn't be an issue now.
Source: Inside of You