Chris here...
Hmmmm, I'm definitely not convinced that Primus is Eternia in the future - sure, Primus is in Eternia's future, that's a 100% given, but I'm not convinced that it is the same planet. My suspicion is that it was a concept that Jack Olesker was kicking around and it made its way into the scene with Hydron and Flipshot in the pond, but I would disagree that it's obvious, I think it's very much open to interpretation.
I agree that the Snake Mountain decaying scene is one of the best pieces of evidence to support the theory that Primus is Eternia in the future - but, until I heard this theory, I always took it as a symbollic illustration of the prosperity enjoyed by Eternia (heralded by the Sorceress) once Skeletor had left the planet. As a kid, I always thought that Snake Mountain crumbled upon Skeletor's departure of Eternia (in other words, that what we see on screen happens in "real time" and is not an illustration of something that takes place over years), although I don't hold fast to that now.
I remember that you and I have debated this before, Dave, and it was very much a case of "irresistible force meets immovable object"!

Whilst I agree that there's a strong case for Primus being a future Eternia (and I would say that if it was, I actually really like the idea!), I think there's also a case to say it wasn't. Until someone senior from either the NA cartoon or Mattel steps up and says otherwise, I don't think we'll ever know for sure!
Take care...
