Sting wouldn't have to be heel, and he wouldn't be. Fighting Taker at mania can be more about "hey, I'm gonna break the streak because I'm awesome" than "hey, I'm gonna kick your ass because I hate you and I'm a cowardly bad man." See also: HBK/Taker.
Anyway, forgot about Mistico. The vignette could be for him too. Kinda doubt they'd put him on TV this quickly though.