Post game content would be an amazing addition to the series IMO. The one thing that has always bothered me when finishing a Zelda game is how little time it took me to do so compared to other Action Adventure/RPG games. The reason it takes so long for other games to have fully "beaten" them (if you even can do so in some cases) is the sheer amount of post game/side - content we can find. Which I would single out as the Zelda Game's main problem, lack of content. The solution does not seem to be that hard either, there are a wide variety of things the series could incorporate into their games to make them live longer; Sure it's hard to add these things but my point is that the ideas are out there, Nintendo just has to use them and/or take inspiration from them to make their own ideas.
We have mini-games that we've seen in almost every title, the sword challenges in SS & MM, shooting gallery in OoT, bombing pots in TP, Cucco hunting in TMC & OoT and a bunch of other stuff. The things I mentioned here didn't even scratch the surface of the mini-games we've seen throughout the series. However my point is that Nintendo could most likely add updated versions of every single mini-game we've played throughout the series in Zelda U since memory won't be a problem with the new console.
Then we have collectible quests, which IMO are poorly made but fun nevertheless. This includes heart piece hunting (all games), golden skulltulas in OoT, rabbits from ST, masks in MM, treasure chests TWW, golden bugs & poe souls from TP and some other ones. Now my main problem with these quests would be that their rewards are pretty lame, let's take TP for an example; we get an infinite source of money after collecting all of the poe souls. Now what good will that do when we have nothing to spend it on and the only thing in the game that consumes money is also partially useless because we only have somewhat of a use of it in the Cave of Ordeals, which (IMO) isn't challenging.
Now compare this to just the amount of side content you can explore in Skyrim (Note; I don't want Zelda to turn into Skyrim but some inspiration for it's side content would be nice). Skyrim has more side content that main content, that's just how much there is, if Zelda were to at least have side content as long as the main quest in a game it would be a huge step. And this is definitely possible now on the Zelda U considering that the console is more powerful than a Xbox 360/PS3.
I'm not here to just moan/complain/cry about the side content of the Zelda series because I do have some ideas for how Nintendo could fix their situation (if they even have on I guess), but I wish that side content in the series would have more time, money and development put into it. Even MM the game that I consider to have the best side content out of all the Zelda games is pretty lame compared to modern day games like Zelda. And yes I know it's an old game but that is exactly my point, a game that is over 10 years old hasn't been beaten in quality side content (and quantity to I guess). It feels as if the Zelda series is slacking because of this even compared to itself, I'm at this point not comparing the game to Skyrim, Dragon Age or Darksiders. I'm comparing the series with itself and it hasn't improved that much in terms of side content.
So how do we (they) fix this? :yes:
Well, as I said in the beginning of my post the solution is already out there Nintendo just has to use it. Something I personally see could improve the series's lore vastly is to add lore objects/quests, these are quests/books that explain some of Zelda's lore (lore = knowledge/story) and could give more stuff to theorize about and/or clear up plot holes/mysteries; for instance a quest that explains the mystery of the Lost Woods or a lore object that explains the Civil War?
Then we have the mini-games & collectible quests I mentioned, just make them more rewarding. Maybe expand upon SS's way of upgrading stuff and it's economy by adding proffessions to craft equipment, weapons and items? or add a bunch of vendors that sell this stuff. To expand upon this maybe include rewards that give crafting materials, recipes etc.
A lot of stuff can be added and a lot of it would most likely change Zelda forever but then again, that is what I'd like to happen at least on a small scale. However they can also just stick as much to the formula as possible in the end I don't really care as much as it might seem in this post because I'll always love the series and play it since I have this magical invisible connection but I welcome change and always will!