Like what? I think the current endings are fine.
2. Put a co-op where if you or your partner die, you have to start from the saving point
Nope. There's never going to be official multiplayer. It'd destroy the scare factor of the game, not to mention the implementation attempts in the past which all fell flat.
3. Revamp SCP-1499 dimension
That's vague. In what way should it be revamped?
4. Put back scrapped/removed SCPs
Nnnnnnope. They were scrapped for a reason.
5. Add new items (backpack/flashlight that replace the nvgoggles in the SCP-939 room/new SCPs (ask help for the people that make mods
))
I can't say what new items, if any, are going to be added to the game, as I myself don't know. However, I do know that the blue variant of the night vision goggles makes a flashlight redundant, since they allow you to detect entities at a distance regardless of if you can actually see them. Also, the developers don't need help, as far as I'm aware. (feel free to correct me on this one if I'm wrong)
6. Add some hidden easter eggs
Like what? There're already plenty of easter eggs in the game.
8. Add SCP-999, SCP-207, SCP-005, SCP-002, SCP-018, , SCP-002, , SCP-053, AND WHATAVER YOU WANT
999: An orange blob of slime which tickles you? Seems pointless.
207: Cola bottles stuffed with more caffeine and sugar than normal? Yep. Seems like a "use this item to kill yourself!" situation. Likely useless.
005: Too powerful, and with the way it works, it'd make 860 completely pointless. Regalis already rejected this SCP when implementing some BOH (Box Of Horrors) stuff into the game, so I don't see it making a comeback.
002: It might be a cool SCP, but I don't see any meaningful way it could be implemented. Only useful SCPs or active threats are considered for the game, I think.
018: Similar to 002. (BTW, you put 002 twice)
10. Make SCP-680 been a threat (having his own containment chamber/see him walking in the facility/that he can kill you)
Firstly, it's 682, not 680. Secondly, that would be a rather large undertaking, considering there were once two models in the works with both being abandoned. As far as I know, an arm is all you're going to get.
12. Put SCP-330 as a object that boost your sprint/blink meter
Eyedrops and the super gas mask, anyone?
In all, there are one or two suggestions which I think could work, but if you were more familiar with the game and its shifting design choices, you'd probably see why the rest wouldn't work in the way you think they would.