Onslaught will be an epic new expansion encompassing all the main NM's from past expansions. I would like to see it be a new area that you would have to fight seriously hard NMs to even get to. The main target being a wicked castle, maybe golden or something of that nature.
Upon arrival at the castle the scenario would play out something like a Bruce Lee movie. First floor would contain Seiryu, Byakko, Genbu, Suzaku. The climax for this phase obviously being a fight against Kirin. Perhaps the second phase could be Sea based mobs eventually leading to a battle against Promathia. Ide like to see the Ark angels included in this phase. Third phase would be ToAU mobs resulting in a final battle vs Alexander and Odin. Fourth phase includes WotG NMs and final battle against its main NM,(havent done alot of WotG). Fifth phase being a battle against Abyssea boss' and Caturae. Sixth and final phase would be a battle vs Altana to test your worthiness to exsist in all these realms. It would have the ability to summon any NM or God at random two at a time.
I am well aware of how vague this post is. For good reason. This post is to spark discussion about a new expansion, and I feel many posting their ideas on this post would be better than just me alone typing out exactly how I think it should be. Please comment on thing like rewards systems, foe battle tactics, and area design. Maybe even post about new gear and weapons items.