It'll never happen, but either Castlevania or Senran Kagura would make a good match IMO.
Senran Kagura might seem a strange suggestion, seeing as it's basically DW, but I mean with the full battlefield-in-motion gameplay, with the main characters acting as generals etc.
Castlevania could work if the storyline involved a sort of time-distortion like that used in Warriors Orochi (or Castlevania Judgement for that matter), with Belmonts and others leading troops of different soldiers against Dracula's monster legions.
That said, what I would love in any future Musou game would be for the developers to figure out a way of players adjusting their allies' troops/strength so that battles don't turn into a series of stalemates with you having to run around saving one ally after the other from gradually losing battles (unless it's a pre-programmed rout due to plot reasons). It's long overdue.
