My hopes are, that with 2nd expansion (don't care about theme) we'll get mechanics like graveyard, card order manipulation (put on top/back of stack) and maybe pick from top 3 (discover like) instead of draw or some sidehand ...
Paladin: I would like to see more support for a midrange/control paladin, the OTK paladin before the rotation was really fun. Warrior: I miss some control cards like Ravaging Ghoul and it would be nice if Deadly Arsenal could become playable, but some tempo options that support rush cards would still be good. Maybe shift to a playstyle similar to Darius Crowley's in monster hunt. Hunter: I guess dragon hunter is the next step, although I don't think hunter should ever become a control class. Priest: High health minions with healing synergy, sort of like in the vanilla hs days, maybe if odd priest became viable. Mage: Cards like Toki and cards from the taverns of time seem like really fun, a playstyle similar to Infinite Toki from monster hunt. Warlock: I'm really sad that control warlock got hit so badly with the nerfs, maybe some sort of midrange demonlock would be nice. Rogue: Kingsbane and miracle decks are more suited to my taste than tempo and baku decks. Druid: Druid is in a good place right now, I'd like if Hadronox druid had an alternate win condition so you don't auto-lose against control mage or shaman. Shaman: Shaman is all over the place, I just wish it would be more consistent rather than randomly generated spells.
Support for recruit warrior, and more whilwind effects like Ravaging Ghoul, Blood Razor, and Warpath. Also, more support for quest paladin with buffs that aren't completely negated by silence (e.g. also summons a minion, or makes the minion elusive, or also has immediate impact on the board).
Working control deck for paladin - maybe with dragons? Some stable win condition like n'zoth.
Less powerful aggro cards. No release of cards like spiteful summoner. Also please stop with those mana cheating cards - big hunter, cube lock - it's just insane and unhealthy. I like the idea of summoning big minions but at least make it so that it happens at least on turn 10, but preferably later and so it actually REQUIRES some setup and not just 2 cards in hand = gg turn 8.
More great control tools like priest aoe dragon.
Something more sophisticated that will force new kind of decks like even decks, taunt druid. Just some interesting cards with strong effects and not give +1/+1 to a minion or summon random sth.
Overall I want to see more good things this meta has provided (talking about strong control decks) as well as midrange and aggro decks having lower WR than control decks so you're actually getting rewarded for thinking and not playing on a curve with only 1 option to choose per turn.
Druid: I really like token druid, but it's good in the way it is now. However, I miss Old School Ramp Druid (just need legendaries or big cards strong enouth and maybe that deck includes Hadronox for some sinery, but less needed than the current deck).
Hunter: Spell Hunter and Recruit Hunter are Awesome; I really enjoy playing them (and against even). So I would like to see them good enouth in next meta, and add to the deck pool a dragon hunter or a Hunter that siniergies around Dire Frenzy (in a MidRange or Combo Deck, maybe?)
Mage: BigSpell Mage is cool as it is, I just want to Elemental Tempo Mage or maybe a Dragon Mage were more powerfull.
Paladin: Dragon Pally and Even Paladin will be, imo, the future of pally; but I want Control Pally to be powerfull (as in the first months of WotOG).
Priest: No Dragons for priest, please! There were a lot of years of dragons in priest, needing them to be playable (almost since TGT). Deathrattle Priest should be the go to, but it will be cool to play a Fatigue Priest, Odd Priest or, most likely, Lyra Priest (as in the Un'Goro era with a priest filled with spells Lyra and Medivh), that would be perfect.
Rogue: tired of Tempo rogue and Keleseth in the class. The Miracle right now is cool, but I just want to Thief Rogue to be viable (not Tier 1, that would be upsetting), and Kingsbane/weapon Rogue need more improvement. Also, if a Tempo Rogue should exist, I just want it to sinergyce with Stealth minions.
Shaman: Elemental Shaman, please, thats how Shaman should play. Control Shaman was so cool, in the past at least, so it's a necesity to have Control Slaman in the meta.
Warlock: I miss Zoolock as the go to aggro/cheap deck. Also, I miss Controllock :(
Warrior: Rush warrior is crazy cool. Is my favourite Tempo/MidRange deck, so my vote is for Rush Warrior to become meta. Also, I miss Classic Control Warrior and Fatigue Warrior (LoE era).
I would love to see a "pierce" mechanic. For example attacker has a 5/5 minion with "pierce", kills the 3/4 taunt minion and the remaining damage goes to opponents face. - that would be probably too broken though and hard to balance around
I'd like to see a meta with less taunt and more end of turn effects for all classes.
A couple of new heroes, like Hagatha would be well received.
Another thing i'd like to see would be a hero/weapon silence. On heroes it would remove armor, extra health (priest amara battlecry for example), maybe a "can't use hero power for next 1-2 turns". On weapons it would just negate the weapon's extra mechanic without destroying it.
As far as themes are concerned, I'd love a zandalari/amani/gurubashi troll theme, or something inspired from WoW's battlegrounds/arenas (would match BfA 100%)