Hear me out, here.
The Smash Bros reveals have generally followed a pattern of characters being announced in connection with franchises either being announced or released. So which franchises have yet to be mentioned for Smash? Ice Climbers, F-Zero, ROB, Game & Watch... and Mother/Earthbound. Despite being a franchise that had two representatives in Brawl, no representative has been confirmed for Smash Bros U/3DS.
This isn't the only evidence, though. Earthbound was released on VC last year on the Wii U. This fact in itself isn't particularly notable... what is notable, though, is Nintendo of America's decisions with regard to their website. Earthbound got its own subdomain, earthbound.nintendo.com. As far as I can see, no other VC title has received its own subdomain, with subdomains usually used for new retail releases, like http://fireemblem.nintendo.com/ or http://goldensun.nintendo.com/ - so why did Earthbound get its own subdomain?
When Earthbound was released on VC, Reggie was asked about the possibility of a Mother 3 localisation, and Reggie's response was essentially "we have nothing to announce at this time". In 2009, Reggie said it wasn't in their announcement schedule - this suggests that it wasn't something they were anticipating an announcement for, any time soon. In 2013, it's "nothing to announce at this time".
And one final bit of evidence. Nintendo recently trademarked "EarthBound" in the US... after the release of the VC game, not before it. The trademark wasn't granted until January this year. The timing is curious, in my opinion. For comparison, Game & Wario was trademarked in September 2012, and Donkey Kong Country was re-trademarked in June 2010, a few months before release of DKCR.
So what do you think, does this point to a new Earthbound game being announced at E3? Note that I don't expect it to be Mother 3... I'd expect that to keep its "Mother" name, to be honest.
