A new trademark named "Delta Emerald" was filed on May 2 in Japan by Nintendo, says Gematsu.
As you likely know, Pokémon Omega Ruby and Pokémon Alpha Sapphire were announced earlier this month for Nintendo 3DS, coming as remakes of the GameBoy Advance originals. Pokemon Emerald followed these two in the timeline, so maybe we're looking at another remake coming down the line for 3DS.
Or not. Sometimes trademarks are just covering bases.