Let's go a step further in predicting the next few month's of reveal and assume that, with so many high-profile games and game anniversaries, there will be two reveals each month until the end of the year:
October: A Pokemon character for Pokemon X & Y (P. Trainer, Jigglypuff, Lucario, Mewtwo, and/or a newcomer are all likely, and we don't know which Sakurai would go with); Sonic for Sonic Lost Worlds
November: Zelda for A Link Between Worlds (As somebody pointed out in another thread, the anniversaries of both the Japan and International releases of Ocarina of Time are the days directly before and directly after (respectively) ALBW releases, so a dual Zelda/Sheik reveal is relatively likely); Captain Falcon for the anniversary of F-Zero's release (which also, cooincidentally, is on the 21st, same as Ocarina of Time [Japan]) OR a Mario series newcomer for the International release of SM3DW (Toad?)
December: Diddy Kong for Topical Freeze (A DK newcomer, either Dixie Kong or King K. Rool, is also possible but an outside chance); A Mario series newcomer for the Japanese release of SM3DW (more likely than the above, as Sakurai has so far seemed to mainly time his reveals around the Japanese releases or anniversaries)
That's as far as Veteran series go, I am unsure of anniversary dates for likely newcomers' series.