A True Single-Player version of the game: Just you and the world. If you want to play with people, that's what the sub is for. While the sub is active, you can seamlessly switch between online and offline modes.
Some of the mechanics needed to do this already exist in game and more specifically, Starter Edition Accounts and PTR. The Dynamic Scaling introduced in Legion certainly blew the door open in that regard. They wouldn't really have to change much, either. Offline Mode would just build off of all three.
Here are some of the changes that would need to happen for it to work:
- For Dungeons and Raids, you're joined by NPCs instead of players. When doing old content or after the first clear, you're given the option of going it alone or being backed up by NPCs.
- You can copy characters from the Online Version to the Offline Version. The reverse would also be possible but you would be prompted to overwrite one of the two if one exists already on the server.
- Certain achievements (PvP as well as some Raid and Dungeon Achievements) would remain exclusive to Online Mode.
- Certain gear (ie. Legendaries some Some Epics) would remain exclusive to Online Mode.
- Instead of getting disconnected, the game will switch to Offline Mode when the connection is lost. If you were in an instance when you lost the connection you'll be booted from the instance. When the connection is reestablished, you will be able to return to the instance if it is still in progress.
- Certain Online-Only Features can be accessed from Offline Mode. Specifically Mail, the Auction House, Battlegrounds and Arenas. If you have no active sub, you will still be able to use the mailbox but will have limited use of the AH.
- The Max Level gear you can get in Online Mode will always be better quality than the gear you can get in Offline Mode (Highest would be Normal Raid Difficulty quality).
- The Collections UI would be seamless between Online Mode and Offline Mode.
- There will be a hard cap of how much Gold per week you can transfer between Offline Mode and Online Mode but not the reverse (250,000G sounds reasonable).
- You will have increased storage in Offline Mode.
- Pre-Expansion Events and the Darkmoon Faire would be Online Exclusive.
- Certain Holiday Events would either be Online Exclusive or work differently in Offline Mode.
- In Offline Mode, Non-Healer classes will have additional options available to them. For example you could buy a potion that passively heals you for a set amount of time. You can also buy an item that will allow you to rez you at death.
- You will be able to gain rep with Alliance-exclusive Factions as a Horde race and vice versa up to Honored. When Honored, you will be able to enter the opposing faction's cities and outposts for commerce, questing or hiring Adventurers of that Faction.
- You will be able to attack the other opposing faction's NPCs by flagging yourself as "Hostile" (instead of PvP). If you are Neutral or Above with the opposing faction, you will lose reputation with them. This can have ramifications when questing on contested zones: Cause enough damage and kill enough people and a bounty will be put on your head! Defeat the Bounty Hunter sent to kill you, you can cut a deal with him: He smooths things over with the enemy faction but for a price. If you agree to the deal, your Rep with the hostile faction will be upgraded to "Cautious" (below Neutral) so you won't be attacked on sight when near their outposts.
...In short, efforts would be made to make Offline Mode and Online Mode feel like separate experiences. Offline Mode would mostly be for those who just want to enjoy the story on their own and quest at their own pace without competing with others or worrying about maintaining a monthly sub. Everyone would have access to Offline Mode since all of the necessary data is already on your hard drive.
There would also be some features exclusive to Offline Mode:
- Adventurer's Guild: Hire NPCs to join you on your adventures. Unlike the Draenor Bodyguard, they will join you in Dungeons and Raids. When certain conditions are met, you will be able to hire your Characters from Online Mode to join you in Offline Mode. You can have up to four travel with you. If you're killed in the field and there is a healer in the group, they can rez you. Otherwise, the surviving NPCs will guard your body for the corpse run.
- Dynamic Reputation System: Your standing with certain factions means a bit more in regards to NPC interactions. Getting Honored with the Argent Crusade will allow you to recruit their Paladins in the Adventurer's Guild. Becoming Revered with The Undercity will net you discounts from all vendors and shopping opportunities. Being Exalted Stormwind City will mean every NPC of that faction knows who you are and will greet you with a bow or a salute. In addition, you can take on lucrative quests for Gold, Crafting Mats, EXP and Gear.
- Personal Reputation: Trust is important. The stronger your standing with certain characters, the better the benefits. Become a Comrade in Arms with someone will allow you to hire them to join you. Becoming a Regular Customer nets you a discount.
- Relationships and Family: I think they'll be able to do this without upping the rating to M. It's all on how it's done, really. Once you raise your Personal Reputation with someone to a certain level, Bonding options become available to you and yes, this includes same-sex realationships as well. Your partner joins you on your adventures but they'll hang around one of your Outposts or a Capital City when they're not with you. You can also "create" children. If one parent is unable to have kids because of their race (Undead) or Class (DK and probably DH as well) you can just adopt. When your spawn reaches a certain level they will be able to join you on your adventures. Once they've progressed a bit further, you will have the option of making them a playable character.
- Hero's Outpost: Your own place in the World of Warcraft. Once you've done enough progression in most zones, you will gain the ability to establish an outpost. This unlocks additional questing opportunities for you and your NPC allies to take advantage of. It will function similarly to the Draenor Garrison in short though it's a bit more automated. Sending your forces on Missions allows them other means of improving but they could also return with new questing experiences for you. For example, let's say you send a Rogue into the Deadmines but he ends up getting captured. You get a ransom note sent your outpost. You can either pay the ransom to get him back or personally go get him yourself.
- Personal Airship: This will clearly cost quite a bit of Gold and take some time to build. Once it's built, you will be able to cruise the world in style. They also come with a team of Mages who can translocate the Airship to Outland and Draenor. In addition, you can assign followers to man the ship or even call down an airstrike.
- Fight for the Horde/Alliance: Instead of PvP, Max Level Players can engage in a progressive compaign against the opposing faction. There are several tiers with the final tier pitting you against the leader of the opposing faction. Win and you become a legend. Lose and you will be imprisoned by the opposing faction. In this case, you will need to switch to another character to free your character. Switch to a character of the opposing faction and you can pay petition for release. Switch to a character of the same one captured and you can launch a daring rescue mission to get them out.
...My head cannon went wild as usual there. LOL. Feel free to ask me anything ^_^
Anywho that's the case I'm making. I have a pretty good idea of what the reaction will be but I will not stop petitioning Blizzard to go this route.