Up until Pokemon Platinum on the DS we always saw our Pokemon games in groups of three, Red, Blue and Yellow. Gold, Silver and Crystal. Ruby, Sapphire and Emerald. Diamond, Pearl and Platinum. While this may have always been the case the remakes of these games have always come in pairs being absent of that third major game.
This case may be ending however with a new trademark that has been filed in Japan. Now before I say more this may have only come to light today but it was actually filed on May 2nd but could be hinting at a third remake. Delta Emerald has been trademarked and this could mean Nintendo plans to give us an enhanced version of their upcoming remakes Omega Ruby and Alpha Sapphire.
Then again I could be reading to much into it and they have just been covering all their bases and taking the trademark as part of the combination, but just given the careful choice of a name they really could be planning this game, I can't say for certain for some Pokemon fans it is but merely a pipe dream that they would like to see. If any more news on this matter comes to light I will let you know until then I announce that speculation season is open. Have fun.