Seems like they're preparing a new part of Time Temple.

Then they'll make a prequel, just like what they did with Vindictus and Mabinogi

Actually that might not work either. The ONLY way MS2 would actually pay off is if it's set in an entirely new world, new dimension and everything. What NEXON has done with the Temple of Time(and if they finish off Elin and make a past world) is make MapleStory have a sequel and a prequel inside it's OWN game. Think about it(just forget about the future dream world thing for a minute). If MS2 was really gonna be a sequel we would just end up with the world destroyed like the Temple shows us. HOWEVER we already have that. So making a sequel off of that is rather pointless because we already have it and can be expanded upon very easily. Secondly in regards to the past. If that file someone had of what looked like past Leafre shows up, then you have your prequel. The world of the Black Mage. NEXON could even take it back further in time from there. When Elin finally gets touched on and completed, you have your past world right there.

tl;dr:
1)NEXON made MS one of the most complete MMOs adding in both the past and future in its gameplay, not just hearing stories of it.
2)Ms2 would only work if it's in a different dimension and world