Makes senseif you ask me, they already did the sentai special (All of Gokaiger) and the Kamen Rider special (Let's Go), but they need one for both... And what better than a "Super Hero Wars" movie?
Although Momotaros is confirmed, but no Ryoutaro? Are they really trying to dump Ryoutaro from being Den-O now? I mean if you can't get "Adult" Ryoutaro(who's doign Rionin Kenshin or however you spell it) then surely you can get the kid who played "Kid/Younger" Ryoutaro