I think, if the data is still there, hopefully they will release all of them this gen. I can understand it being there last gen in case they want to reintroduce them through event or something (and being the case this gen again), but if it's still in the code I hope they show up eventually.
Gems were among my favorite hold items, so I was quite dismayed to see Game Freak had nerfed them by making them unavailable. My guess is that they're overpowered but that Game Freak is having trouble finding a way to nerf them without putting their power so close to the type-boosting items like Charcoal and Twisted Spoon so as to be redundant.
For now, there are Z-Moves, which are essentially a roughly 100% boost instead of 50%, only you're limited to one per team. (That percentage varies on a move-by-move basis, but it's a rule of thumb.)
Also the rate is quite low, it's something like 0.05 Pokémiles per day Per Pokémon.
Going in the past to gen 6: I've seen several sites give a estimation of:
PokeMiles Earned Per Day = ( [ Total number of Pokemon in Bank boxes on previous day / 3000 ] * 100 ) - 1
And If you get part of a mile, it would roll over everyday until it completed a mile.
Also this calculation is seems to done at the same time per day as first time you ran the app. (So if you started the app on 10:17am , The "Day" is starts at 10:17.)
The above calulation seems to be off for less than 31 Pokémon.
Looking at that formula, that'd be the equivalent to (A/30) - 1, where A is the amount of Pokémon you had in
Pokémon Bank at the end of the day. A much less complicated equation.