Idea for improving longevity of the game

They should implement a repeatable quest system.
Also, repeatable dungeons, based on quests.
Like having a Thresher Maw boss fight, just as in Grunt's Loyalty Mission, on Tuchanka.
Expand the bestiary.
And give rewards. Good rewards. Not Anthem style shit, where you get greens and blues for a Boss run that takes 15+ minutes.
And FFS, bring back armours and squad customization.
If you want people to grind your game, while also giving rainshower rewards, have that equipment spread out over a team of 12.
Do you know how many times people will do such runs, to gear up their entire squad?
If I could do that, for ME2, I'd still be stuck, playing that game.

Greatly expanding the gear crafting system would help a lot with my own investment. I would love to be able to deck out my followers and create both powerful armor sets and weapon loadouts tailor-made to how I want them to behave in battle. Like if I have a krogan follower, and I want him to look like a savage dinosaur with a shrapnel-launching flamethrower or whatever. To this day, Inquisition’s probably my favorite system in terms of equipping allies, because there was so much I could unlock that made my allies really powerful on the battlefield, my only complaint being the conformity to some kind of weird archetype affixed to each companion, so they always appeared a certain way no matter the armor I made. To add to that, I’d like to be able to take appearance customization to the point where I can bypass any of this “iconic look” garbage and have them appear in battle what I feel best suits them, rather than being pigeonholed into whatever the game dictates, meaning no more retarded breather masks and the sort if I don’t want them.

MP map/level editor!

I don't think I'd do it. Part of the fun with ME is not knowing what your choices will do. Did you know it was better to kill the geth heretics? Could you foresee that destroying Maelon's data could be significant, especially if you were pro-krogan and like Eve? What about if you didn't do loyalty missions in ME2?  I think some choices are pivotal. Not knowing outcomes makes for increased replayability. Now, if you had something show up on a map after you made a choice, something that might suggest there was another unnamed choice you could have made, maybe.

Oh no, I don't think it should reveal what choices you make. Just that there are other possibilities available. A feature like this shouldn't even become available until you've actually beaten the game.

That sounds reasonable. I kind of suggested that but I'd ignore mentioning that there are other choices until after one was made.