ME3 sequel

So can the turian and quarian yet they were squadmates in ME3, if they survived

Heck Chakwas could be dead!

But yeah, what would be done to her character would be a more than valid fear.

I been watching some old ME3 videos on Youtube.  It seems to me the fans have already written a way out of the endings anyway that makes enough sense to use, should they decide that the only way to guarantee a successful return is with Shepard (not that I'm personally against a new protagonist)... I think we are all familiar with it and by it, I obviously mean IT, Bioware said no once, but hey, why not?  How could it  go down?   

So, you start up ME4 importing your save.  It begins a cinematic in the skies above Earth as the Reapers mercilessly cut through the allied fleets, Shepard is on the crucible engaged with the Starchild while it explains Shepard's options, no conversation interaction needed here, its just replaying what happened in ME3, with the dominant Reaper forces in full view outside.  Shepard begins her inexorable limping march towards the machine, an ill defined voice calls out, Shepard stops momentarily but shakes it off and continues.   As applicable to the ending choice, Shepard stops at the crucible core, pulls out her pistol, another voice, louder this time "Stop!".  Shepard aims at the machine, but her arm is dragged away by an unseen force, fighting with all her might she draws the gun back towards the machine, "No stop!  It's working!" Shepard looks around in confusion, to the left, the back to the right to see the Liara's right hand on her wrist, her other round her waist, grappling, fighting to pull her away.  "Look!" Liara's left hand moves to Shepard's temple, locking Shepard's left arm, Liara's eyes blacken and the vista of destruction outside the citadel beings to shift and change, a Reaper ship can be seen outside, clearly in distress, its weapons malfunctioning and miss-firing, moving erratically, it howls as a pair of Turian battle cruisers break it in two with repeated salvos and the Starchild fades from view.  Shepard is overcome by her physical and mental trauma and passes out.   Camera pans up and out of the observation deck on the crucible, into space, through the carnage and enormous field of wreckage outside, the Reaper fleet in disarray, already most are destroyed. then half way past earth, que title and Mass Effect theme music. 

I mean it was obvious wasn't it?  You build a device to defeat the Reapers, then what is quite clearly a Reaper tells you that the only way to destroy the Reapers is the shoot the crap out of the device you just made to destroy the Reapers?  Come on!  All they were doing was giving you three options of disabling the crucible and killing yourself in the process because they were losing and they are dicks like that.  

That's certainly possible. Though one criticism I have with your example in particular is that Liara should only be the person if you are in a romance with her and maybe if you aren't in a romance with anyone. If you are in a romance with someone, I think it would be better if it was them who snaps Shepard out of it. 

Ah, okay. I thought she was the only survivor if you did that since I've never done an "everyone dies" route. 

Having Dr. Chakwas, Dr. Michel, and Dr. Chambers all in the med bay together helping with different things would be fun(as long as they don't ruin the characters). 

I wouldn't want the asari snapping my Shepard out of her daze if I wasn't romancing anyone. I would want space hamster instead

Hamster shmamster. This dude is the only one worthy to snap Shep out of it. 

Could be sure, I just went with Liara, because she has that mental connection thing she does with Shepard from time to time. Seemed the easiest to buy.

If they would make a sequel to ME3, I would like to start with the new protagonist in London being in a ground fight with the classic Reaper forces, trying to survive and save as many as possible. Then just when it looks like my position gets overrun (think of the 5 waves in Arrival), the Crucible fires and I can get out of the dire situation. Looking up at the sky I'm like "WTF just happened?". Then "Vigil" starts playing, the monitor goes black, Mass Effect 4 shows up on the screen and they push forward in time to put me in any post-reaper situation they like to start my hero's journey.

The trick would be preserving the ending/state from ME3, if Bioware could pull that off it would be incredible, its just that damn synthesis ending!  With destroy or control you either have the husks collapsing or in retreat, these would make great opening scenes... Then that bloody 3rd ending that I'm pretty sure next to nobody took, but all the same there would probably be mass outrage if they de-canonised it.