Not April Fools, sorry
River City Ransom SP basically came out of nowhere for me, and was on track for an April release on 3DS. The operative word here is “was,” because Arc System Works has delayed the game to June 2. No other reason was given besides “quality” concerns.
At the moment, SP is a Japan-only release, but something tells me this will be an easy one to import. That is, if you have a Japanese 3DS!