Story:
I'm thinking for the story that you can either retcon some parts of it to allow for it to happen, or change some other things so it makes sense. "unless of course Layla is pregnant or Logan wasnt executed." These two ideas would be excellent.
"Are you just going to ignore the fact that Reaver is still ruling albion whilst the true king is missing?"
That could be a feature in there. Have you try building a guild while he's in charge. A lot of good ideas can come from that.
"And what great existance? Wouldn't it have been mentioned before now?" Well, they can always create something. Maybe take some unknown creature not given that much information in the lore and flesh it out. It doesn't really have to be in the Void, that was just an option. It could come from anywhere, maybe make it a threat that is dealt with in multiple games, like the Reapers in Mass Effect.
World
"An open world such like that of Elderscrolls, GTA and Assassins Creed is far too ambitious for fable. To simply change the whole fable landscape and graphics would be to recreate the game. It wouldn't be Fable anymore; it would be mor like a lesser Elderscrolls game.
To ask Lionhead to incorporate the countries surrounding Albion at well as Albion itself would be like asking DA to feature the whole of Tamriel or asking DA to use the whole of Thedas."
The thing is, if other games could do this, Fable can do it too. They have the resources. All they would have to do is create a new engine for the game. Considering this will hopefully be on next gen systems, that's not such a wild idea. I don't see how it would not be Fable. If it still contains the art style of Fable and the feel of the games, it'll be the same. And Albion is just a country, as far as I know. Tamriel is a whole continent. Plus Zenimax is going to use the whole of Tamriel for the Elder Scrolls Online, so I don't know how that's a problem.
Combat
"Guns are far too effective. Perhaps the incorporation of ammo would discourage the player from overusing a gun and make the game that bit more challenging? No one can just deflect a bullet in an 18th century fantasy setting unless able to use will."
Well, maybe have guns be inaccurate and slow to reload. Like I said in one of these posts. That way, in order for you to get a kill with a gun, you should be close range and use it at the end of a melee combo. It would also make bows and crossbows better alternatives. The ammo system you mentioned is probable a good idea too.
"Also, all trolls in Albion are extinct. They were culled by decree of Logan."
Retcon that. Maybe make it so that a small amount of Trolls survived his order. Perhaps even have a quest where you have to kill off the rest of them.
Weapons
"I'd like to disagree with the Legendary category. I think "legendary" weapons should be accessable throughout the game. Hammerthyst was a "legendary" weapon due to it's past not it's quality and was available at the near start of Fable 2 for example. I'd like legendary weapons to have that rare quality about them; they should be valued as rare equipment again."
I'm not saying that legendary weapons need to be top-tier. I just listed it at the end for the sake of the list. Have a few legendary weapons at the start like in the Fable 1 and 2, but have the best ones be endgame gear. And still have the other weapon types.
Weapon Morphing
"I'd like low quality weapons to be easier to morph and augment but have less impact on the change and higher quality weapons should be difficult to augment and morph but it deserves a higher reward. (I hope that makes sense)."
Do you mean that the weapon augments should be implemented by chance? Maybe make it so that you can fail to augment successfully? That's a good idea. But if they did that, they would either need to make augments cheaper to buy, in case you kept failing to augment a weapon and then lost you augment, or make failing to augment a weapon give lower stats than you would get if you augmented successfully.
Magic
"All spells should be chargable but your body should be more prone to damage when casting. Don't deny people the big maxed out spells!!"
The thing about having each spell be chargeable is that there a lot less spells, due to each spell being versatile. Plus, it kind of screws over constant spread spells, like lightning in Fable 1. Maybe have charge variants for certain spells, but just have more spells available.
Social Interaction
"Fable 2 had it spot on in my opinion. The expression system made the game stand out among other RPGs. It featured something new and unique and made the game more personal. It should be more of a focus for haggling, sweet talking, romancing and intimidating."
The thing about this is, that in Fable 2, the expression system is highly exploitative. Someone doesn't like you? Keep dancing for them for 5 minutes until they do. It was very easy to do stupid things for other people to get benefits. If you want to make someone like you, you should do it through your actions or you responses to them through a dialogue system.
Menu and UI
"I like the breadcrumb/golden trail.. No games that i know of have one."
The golden breadcrumb trail, at least for me and a few others, tended to glitch out some of the time. But maybe having both a minimap and the trail, like you said, would be better, and have both be optional.
"I like the Sanctuary and even though Reaver currently has residence, it's more exciting than a menu and is like a portable chest.. Makes more sense than a hero that can carry a ton of weapons. Perhaps this quick menu shut be a hotkey system labeled backpack or satchel like in the old Ratchet and Clank games and can be changed through in the Sanctuary."
I don't really see how being able to go to the Sanctuary whenever you wanted to made that much sense. Then again, I don't see how being able to pause the game and go into an inventory makes much sense either, so I guess that doesn't really matter. The thing about the Sanctuary was that it was very tedious to access your items on the fly, it was much better for fooling around in that for quick decisions. If Sanctuary is going to be added into Fable 4, it should be just one room (a large one), and give you access to everything you need quickly and easily.
Thanks for giving me your opinions. I'm glad someone took the time to read my huge posts. I just had a lot of ideas that I wanted to talk about.