I would love to see it. GW1 is simply superior to any piece of music from GW2. The GW2 original theme was great, but mostly because it was just a revamped version of GW1 Prophecies theme. HoT was tragic and PoF was so-so.
I don't see the original Factions theme being re-used again, simpyl because it would make Arenanet look lazy. However, the mentioned Prophecies-GW2 original theme revamp-like pathway would be definetely the way to go. Hopefully they do it this way.