Hi,
right now the Endgame is Monliths and Corruption u get items to farm higher corruption to get better items to farm higher corruption until u hit your ceiling… thats fine but kinda exhausting 
My Idea:
New Timeline that is seperate from story etc.
Apocalypse Timeline
Can Bosses: All of the other Timelines + Added Bosses over time Both Normal Bosses and Shades + Special Apocalypse Boss
Timeline Mechanics:
Corruption works as Usual
New Apocalypse Doing an Echo Raises Apocalypse doing a Shade lowers the Apocalyptic Expension* by X levels + add Corruption - Reset Net
Doing the Stability Boss Adds Gaze wich increases the Apocalyptic Expansion Level Reduction of Shade + Corruption gained when doing shade
(U fight the normal bosses + shade to get higher corruption + Apocalypse and to fight the Apocalyptic Expansion wich will make u fight the boss and End your Run (u can also willingly go to the Apocalyptic Boss) (U have limited Trys for the Boss if u dont manage to defeat him u loose corruption gained in that run and u dont get the drops he has + no access to the forge)
Apocalypse gives Chance to Drop Better Apocalyptic versions of Items/Uniques(and New ones) + raise the dificulty exponential instead of Linear like corruption
Apocalyptic Expansion: after X Echos the Expansion will begin from the starting point… first its 1 echo arround then 2/3 and maybe more …
When the Expansion Reaches u Fight the New Apocalypse Boss this Resets the Net + Apocalypse and Some Corruption after the Boss u get Acces to the Apocalyptic Forge
Apocalyptic Forge: U can put items in and they have a chance to turn Apocalyptic if it fails the item is destroyed… Uniques have Lower chance per LP and if they are allready with Stats the chance is lower based on the stats Tiers… cause it will make this stats go up by 1 Tier
Exalted Items have chance based on Affix Tiers if success all Stats are Raised by 1 Tier.
(U can try multiple times once u have beaten the boss but when u left the forge u must do it again) (Also Chance is based on Apocalypse Level)
Apocalyptic items u can Drop have a chance to have 1 or more tier 8 stats…
Apocalyptic Uniques can only be crafted to Legendary with Apocalyptic Exalted items… at the Apocalyptic Forge (Destroying Both if Failed and giving + 1 Tier on all Affixes the item Obtained so the item could have 9/8/6/6 if it was LP4 paired with a 8/7/5/5 Apocalyptic Exalted)
(Apocalyptic Exalted cant be Put into the Forge. only Normal Exalted/Uniques can + to make an Apocalyptic Legendary… (Putting in a Old legendary item will raise the tiers of affixes by 1 Guaranteed but not make it Apocalyptic)