Update: The director of Official Nintendo Magazine in Spain has exchanged some clarification tweets with the publisher of the source story, Nintenderos, simply stating that the 3DS entry still has a Summer release without being confirmed for September. In an impressive feat of backtracking that defies the laws of printed words, the magazine was apparently referring to the Summer estimate — this is somewhat counter to the fact it printed September instead of Summer, but those are the breaks.
Thanks to Oscar from Nintenderos for assisting with translation and clarification.
When Masahiro Sakurai hosted a Super Smash Bros. Direct recently, he provided a Summer release window for the 3DS version. While some may have hoped that the Wii U entry would arrive first, it nevertheless gave us the tantalising prospect of enjoying one of the games in the relatively near future.
It's possible that Nintendo's definition of 'Summer' is stretching the release as far as possible, however. According to the Official Nintendo Magazine in Spain — thanks Nintenderos — the portable entry is expected in September. While that may not fit the season's window for all of us — counting June / July / August as Summer — much of September does qualify in purely astrological terms in territories such as Europe and North America. If true, Nintendo may have been cute with its Summer announcement, albeit arguably a little sneaky.
Of course magazines, even the official variations, can get details like this wrong or make assumptions — the Spanish iteration also suggested Diddy Kong would be playable in Mario Kart 8, which was inaccurate. Until Nintendo provides a definite date, likely at E3, we'll just have to hope it's not too far away.