I've been thinking of something to suggest other than "do what you guys wanna do!" for a while now, and this was the primary thing I came up with. Time/time travel as a major mechanic in a WRPG is something untouched - it's fairly prominent in JRPGs, and tends to be quite well done in those that attempt it, (obvious nod to Chrono Trigger, but also the more recent Radiant Historia and Xenoblade, which are both fantastic games). It would allow you to potentially implement some interesting gameplay mechanics, (protag's faux-omniscience and ability to "change the future" in Xenoblade comes to mind), use multiple different settings, (fantasy/magic? prehistoric? industrial/steampunk? futuristic? contemporary? western? post-apocalyptic? just to name the stereotypes), incorporate multiple different skill-trees/proficiencies and party members with different specialisations according to the time-zone they're from. It'd be like taking the Arcanum formula and going wild with it. Main character a blank slate, able to forge it into whatever you please, whether it's a gun toting magic wielder, a smooth-talking cyborg, an engineer skilled at sword-play, etc. etc. Scope would be potentially massive, spanning different time-zones, multiple different areas, actions in the past affecting those in the future - it could be quite interesting. Real-time with pause(...and rewind function?) - or turn-based? - isometric RPG! I could go on and on, but that's the gist of the idea.
Hope this suggestion isn't too late to add to the pile!