Well, the BW starters had to wait one and a half generations to get their Hidden Abilities even though they were introduced in the same generation as them...
Yeah, but GF seems to have gotten faster about getting HA's out starting in Gen 6, with only the Skrelp, Clauncher, Tyrunt, and Amaura lines being the only non-Legends/Mythicals not to get theirs right away, and all Gen 6 Mons having their HA's released by the end of the Generation.
At the moment, it's just the Starters, the Tapus, and Passimian/Oranguru (actually, can they be SOS'd now?) that are unreleased, and with USUM being the last games on the 3DS, there may not be much time left to get them out (though I wouldn't be surprised if the Telepathy Tapus rollover into Gen 8), so I'm curious as to how/when we'll get them.