While one of the series’ core features, it may be for the best that it appears that HMs are not going to be a part of Pokemon Sun and Moon.
HMs (Hidden Machines) in previous games taught Pokemon a specific move, and could be used repeatedly. TMs (Technical Machines) did the same thing, but were one use. The main reason HMs existed were because the 8 HMs you got over the course of a game were tied to progression in the overworld. For instance, you couldn’t ride on water to reach islands until you learned Surf, or get past certain trees (really?) until you learned Cut. This made it possible to hide items in the very beginning of the game until the player could return with the right HM, much like how Link would have to return to areas with new items in The Legend of Zelda to collect everything.
The problem was that these HMs took up 1 of a Pokemon’s 4 valuable move slots, and generally, HM moves aren’t the best possible moves in the game for battling. Many players would have one or two “HM slaves” that they taught many HM moves to and kept in their party for progression, but didn’t really use for battle. What this meant was that for a trainer to have all 8 HMs available, she’d need at least 2 HM slaves in her party of 6.
The new game has you summoning “Ride Pokemon“, which we new about, but the demo has you doing this instead of using HMs; for instance, you summon a Tauros to use Rock Smash. In addition, the demo, which has been datamined for way more information than Nintendo likely wanted us to have, has no information about HMs.
This is an interesting shake-up to the series, and given the inherent limitations of HMs, one of the best possible. We’ll have to see whether they find another progression blocker, or make the game more open-world, when Pokemon Sun and Moon release November 18th.