Nintendo has applied for rights to a previously-unannounced StreetPass feature and it has references in it related to the 'weapon fusing' found in the new 'Kid Icarus: Uprising' game
A patent which credits Masahiro Sakurai as the inventor has alot of details in it as outlined below that covers alot of the unique gaming elements found in the new Kid Icarus: Uprising game, but since this patent was filed by Nintendo last June and published finally on December 29, 2011, it looks like Nintendo has bigger plans for this 'weapon fusing' idea more then just using it once in Kid Icarus.
patent details a feature for an unspecified shooting game
patent involves transmission between two systems
includes a process for fusing pairs of in-game weapons together
each piece of data in the exchange represents a weapon
when two systems meet, this weapon data can be fused into a new weapon
fusion costs coins
weapons set to transmit cannot be equipped by your character
a gun and stick can fuse to create "a weapon capable of firing and using magic."
weapon stats are determined randomly from a pre-specified range
these include attack power, elemental ability, stamina, shooting range
fusion is not limited to StreetPassed weapons
fusion can include two weapons found in treasure chests in single-player play
This is no doubt it is related to Kid Icarus: Uprising. It's just funny to see a patent directly related to this fusion system, I guess Nintendo does not want any other 'gaming' platform to steal their idea.