Dual type moves- I know people already suggested this and some found it difficult to find a solution. It's simple, thunder rain - electric/water, calls out a rain that powers up water type moves for 2 - 5 turns and strikes the opponent with thunder on the first turn.
Or Dragon Thunder - Dragon/Electirc, simply one strike with 150 power. Weakness and Resistance to Dragon and Electric apply at the same time.
Better Pokemon designs, this is just my opinion but I dont feel proud of myself when I do so much in the games and go on my adventure defeat strong opponents with crappy design pokemon, again it's just me.
Pokemon apps - i'm talking about something like what we got in Platinum, I found it very useful such as the item finder and the steps count.
It would be really nice if they could make some real time apps. For example a dream radar app for the phone where you could access dream radar via mobile phones. They could have other apps too which could have enjoyable features such as the Pokemon Amie, an app that lets you buy, sell accessories, character customization, trade rare items which could only be achieved by this method and so much more which then could be applied in game from the apps.
A good storyline, longer game with good gameplay mechanics and more exploration with rewards.
More Pokemon being obtainbale in a unique way - Most Pokemon are not that hard to get, in black 2 and white 2 I was able to get almost all of them by trading. Now this is good but think about how rewarding it will be when you go on a quest to get an item, then that item on a different place which opens a cave, explore the cave which gives you a hidden TM that lets you access an area in a different side of the map which contains a rare species of Pokemon now ofcourse this is all optional. They should some Pokemon extremely hard to obtain this is just my opinion but it makes me feel special about my Pokemon.
Can we carry 8 - 10 Pokemon with us? Atleast 8 because there are so many Pokemon that weball love. Fair enogh we can't use them in battle but atleast carry them with us and able to switch them into your party outside of battle. This can make training a lot easier.
In Univa we learn that there are more than 8 Gym Leaders. Why not do the same in game but you only have to beat 8 to gain access to the Pokemon League, defeating the rest gives you additional rewards.
More items that is useful outside of battle such as the item finder, it will make the gaming experience fun besides the battles.
Need a Rival like Silver - Ok people might say a lot for this one but think about it it's been too long since we had a rival like him, the new ones are so friendly and cheesy. We need a badboy like Silver or atleast Blue.
Items that you could have to your Pokemon that works in different unique ways changing the battle style to a unique way apart from factors like type and stats. Also these items should be achieved in a unique way like online rank battles, exploring hard dungeons/caves, dlc etc
Customizable profile for online multiplayer
New game plus - well I dont know how this is going to work but every time I finish the game I really dont like deleteing my old game data and starting all over again deleting all my achievements.
Actually the best way to apply dual-typed moves is to have it apply STAB of one type and weakness/resistances of another. For example:
Scald would get Water STAB but act as a Fire-type move. Not saying Scald SHOULD be dual-typed, just an example.
Of course it'd have to be very limited. It'd be annoying for every punch move to now be part Fighting, it would ruin the concept by making it super common.
When you start having dual-typed moves, you run into trouble with dual-type Pokemon using these dual-type moves (how would STAB work) against other dual-typed Pokemon (calculating overall multiplier ourselves would be a nightmare) and even worse when you throw in abilities like Thick Fat or Dry Skin.
Dual type moves are a terrible idea because we don't know how it'd work.
What happens if both types are supereffective? Does the target take 8x damage? 4x damage? 2x damage? What happens if one type is super effective, but the other nullifies it? Does it take no damage? What happens to abilities like Water Absorb, Volt Absorb, etc. when it's a dual type move, especially when a poke is immune to one element but weak to the other?