All the while, Malcolm tinkered with sorcery and witchcraft to make a nifty little talisman, customized to steal anything it’s wearer desired. And what Malcolm desired most was Barry’s life—and by extension—super-speed. But then Barry had to go die saving the universe before Malcolm could actually use the talisman. Denied his true revenge, Malcolm decided that the next best option was torture upon Barry’s descendants. So, one spiffy blue costume later, and Malcolm declared himself Cobalt Blue and used the Talisman to steal Wally West’s speed (for a little while, anyway).
With Malcolm's comics history in mind, it’s easy enough to think that Eddie is Barry’s long-lost brother on The Flash. The two appear to be close enough in age, and Henry Allen has a pretty good reason to not tell Barry that he has a (presumed) dead twin. And that…whatever it is around Eddie’s neck seems to have the appropriate size and shape of a talisman. Then there’s the “Thawne” name, tying Eddie to the corrupt family that raised Malcolm. But considering what a nice guy Eddie was on the Flash, the show would have to do some work to make him want to attack Flash—after they bring him back from the dead, of course. Given the The Flash's love for the supernatural, however, the show's writers could easily create a tidy explanation for both Eddie's resurrection and transformation to mystical superbeing.