Say, if by some wacky event you guys suddenly gets the position as the lead writer for Mass Effect 3, how would you guys write the circumstances of the Reapers' defeat? I am interested in hearing various ideas that all of you might have. Your own version of the Crucible, if you will.
I think the tricky thing is having a weapon that can defeat the reapers without it being a massive arse-pull; i.e. have it based on concepts already raised by the series. Finding the schematics to a prothean superweapon on Mars, despite anything cool you do with it later, is an arse-pull.
Given that in ME1 we established that the protheans can build small mass relays (and that the allied forces have access to Ilos, even if the VI there is non-functional presumably a hand-built prototype relay is easier to reverse-engineer than the full-size reaper-built ones) and that in ME2 we established that dark energy is a huge thing (srsly, I'm playing through ME2 atm and if I'd taken a shot every time someone mentioned or alluded to dark energy I'd be on the floor by now) that can fuck
stars over, I think combining the two would work. A pair of mini-relays, one at Haestrom (guarded by allied geth and/or quarians) and one at Earth or wherever (slung on the Destiny Ascension, guarded by the rest of the multi-species fleet) that would draw dark energy from the dying star, throw it across space and sling it at a reaper. Give it a bit of a charge-up time to determine how many of the reapers surrounding Earth it can take out before getting overwhelmed, dependent on your EMS, and boom: you've got your super-weapon, no arse-pulls required.
Have the purpose of the reapers be to prevent the build-up of dark energy -- like Drew Karpywhatist intended, I think? -- because it's unimaginably destructive to the fabric of the universe and even letting a sentient species get to the point of experimenting with it is dangerous to the future ability of the galaxy to support life and you've got your post-ME3 setup, where the Spectres are retasked to hunt down anyone experimenting with dark energy, the scattered remains of the batarian race are building their own dark energy superweapon to get their revenge on the galaxy that abandoned them, whatever.
edit: Ever since we were simultaneously disappointed by the ending my other half and I have been throwing around ideas for a better Mass Effect 3, challenging ourselves to see just how late in the game we can chop Bioware out and still come up with an internally-consistent explanation, story, and ending. My favourite of what we've been throwing around involved the Crucible plans being a Harbinger plant. Harbinger, being an old and experienced reaper, is far, far better at organic mind manipulation than other reapers; it considers, for example, Sovereign's indoctrination of Saren to be the fumbling of an amateur. For many cycles it has been planting the idea for the Crucible, a super-weapon that can kill all reapers in one shot, in the minds of organics. Harby has been doing this because it is convinced the reapers have been indoctrinated by the Citadel AI, which it believes was left behind by whoever created the first reapers to control the cycles and control
them. Harbinger seized Sovereign's failure as an opportunity to test its theory without interference from the other reapers, and built its own reaper out of humans far away from the Citadel AI. Even though it was killed by Shepard, Harbinger became convinced that what it saw of its developing consciousness was sufficiently different to that of a normal reaper that it's theory
has to be right: the reapers are slaves. It decides to put its Crucible plan into action and nudges Liara in the right direction before the start of ME3, leading her to discover the plans on Mars.
The real purpose of the Crucible is to break open the locks on the Citadel AI and let Harbinger in to the low-level Citadel systems, which it plans to use to a) interrogate and erase the AI and b) free the reapers from their indoctrination. The Crucible didn't work properly, however, and Harbinger realises this at the same time that the star child manifestation of the Citadel AI is feeding Shepard a load of bullshit. So as the star kid is finishing off its speech, Harbinger reaches into Shepard's mind and speaks directly to her.
SHEPARD. IT LIES. DO NOT BELIEVE ITS LIES.
Deciding that it's now or never, Harbinger breaks ranks with the other reapers and flies directly towards the Citadel. Shep turns around and sees it come to bear directly outside the chamber.
SHEPARD. TRUST ME. THE CYCLE MUST END. THE CITADEL'S PLAN WILL THROW THE GALAXY INTO A THOUSAND-YEAR DARK AGE. IT WILL REBUILD FASTER THAN YOU CAN. WE WILL DESTROY YOU BEFORE YOU CAN MAKE YOURSELVES READY AGAIN.
I HAVE ANOTHER WAY.
A reaper shuttle lands in the chamber, and Edi is escorted out by several husks. They are holding her but not harming her.
I MUST HAVE ACCESS TO CITADEL SYSTEMS. I CAN FREE MY PEOPLE AND YOURS IN ONE STROKE. THE ARTIFICIAL LIFE FORM CAN DO IT. IT MUST INTERFACE WITH THE CRUCIBLE AND GIVE ME ACCESS.
Then you have a choice:
1) believe Harbinger and have Edi give it access, in which case a non-destructive energy beam is spread around the galaxy by the relays, releasing the reapers from their bindings; some carry on reaping as it's all they have known; a few defend the organics
from the aggressive reapers; others, including Harby who ultimately doesn't give a shit about organics and doesn't bother to stick around and defend us, set off immediately for dark space; and some, overwhelmed with the pain of the dead species inside them, simply fly into the nearest star to die. This ending is kind of bloody as many reapers don't stop their assault.
2) believe the star kid. You get the same endings we already have.
3) choose to believe neither of them, have Edi take over the Crucible systems and fire a non-destructive energy beam that simply shuts down the reapers. Whether she survives this is dependent on your alignment, and whether you have high enough EMS for the Normandy to survive the whole battle (although if it doesn't then you could have Edi transfer herself into the Citadel, surviving but forever mourning Joker).
Sequel ideas: who or what created the reapers? The allied species undergo a technological renaissance as they reverse engineer dead reapers (using remote drones to go inside the reapers as the dangers of indoctrination are now well understood), and prepare themselves for the possibility that there may be something worse than the reapers on its way in to the galaxy.