Actually this does sound interesting.
As another third party enemy such as the Bulblin warband roaming Hyrule field causing trouble wherever they went would be fun to see again. As I really cannot see them ever being much of a large Hyrule conquering threat, or someone would would stay loyal to a single dark lord for too long. They were barely loyal to Zant in TP. The Great Moblin could be brought back for something like this as well, he has only appeared in the Oracles and I thought he was an interesting character. But an optional fight with a roaming party of Moblins/Bulblins would be a great addition to have in a game. Either as a minigame, miniboss situation, or for sidequests to rescue random villagers or people wondering out in the field.
Plus this would bring back the Epona horseback fights from TP, those were great but there were so few of them in the game and none of them were really optional. The Moblin/Bulblin warparty would create trouble in every location they are in and only shoot arrows at Link and ride away each time he came too close. Outrunning Link every time he came after them. So he would have to gain Epona to actually catch them and fight them whenever he encountered the warband in the field. Maybe for some kind of reward each time he fought them. Either more arrows, quiver, or rupees they had stolen from the villagers. They could also be a source of fire arrows since Bulblins used them so often. Each time Link kills a few, he would gain 5 or so fire arrows from the Bulblin.
I would also like to see a flying threat that could appear at any location in Hyrule for an optional miniboss fight such as the Argorok or Helmarock King. They were both seen constantly flying all around in the games that they appeared in. Usually causing trouble, breaking bridges, buildings, or just roaring and scaring Link. They would start out as background characters that are only seen flying overhead sometimes out in the field or near the mountains. Just a part of the scenery in a fantasy setting such as Hyrule. And over time would become more interactive. You could hear them roar once or twice when they came closer to your location, maybe knocking into a mountain causing some boulders to fall that you would have to avoid. Then after a certain amount of time or dungeons were completed in game, maybe after you gain something like the hammer or hookshot to reach them, then they can be met and fought when they are in the same location as Link. They could also drop quest items each time you fight them. The Helmarock could drop Roc's Feathers each fight resulting in Link eventually gaining a Roc's Cape. Or the Argorok could drop dragon scales that Link could use to craft a greater shield or armor from.
And if you manage to defeat the roaming threat somehow (like if it was an enemy), then maybe we could get a big reward or something. The enemy's difficulty and rewards should go up every time you defeat it... Sorta like Jolene from Phantom Hourglass! 
