Real question for me is why? Outside of promoting a possible RS remake which probably won't happen till after XY I don't see them having May return. And also the Special episode Brock got didn't really do him justice either considering he is the companion that spent the most time with Ash during his travels.
As much as I would love to see Haruka back, we already had Hikari coming back in Isshu and Haruka coming back in Sinnoh and Kasumi in Hoenn.
So by following this pattern where heroine briefly returns in the next region, there's no chance of Haruka coming back.
As Kenshin stated, there would be a chance if the RS remakes were about to be released but as we will be having XY I don't see it coming for some time.