The elaborate plan, is just that. The plan. The Reapers sleep, Soverign watches, when he thinks it's time, he pressed the button and the cycle starts. It's just business as usual. And it's a lot more effective, faster, and easier then travelling there, I'd wager, even if they can travel at speeds that could make the journey in our life time.
So I doubt the Citadel's Mass Relay is there because they lack an alternate method of travel. My money is on something like soft warp holes. They appear in the video to be travelling at no greater speed then our spaceships, and still have a ways to go, so it's not something like Hyperspace. Maybe it's the same general principle, but while they are moving at this leisurely speed, space and time warps around them, so that they shoot through. Same as worm holes, really, but slower, and just a random theory.
No need to get all defensive. :'D
I can speculate, too, though ... I was hoping the Reapers would be stopped before even reaching our galaxy.
I'm just saying, whatever explanation they come up with, and I'm sure they're giving it some serious thought, it needs to meet two requirements, that are sort of two sides of the same thing. Basically, it has to make sense ( i.e. the Reapers didn't simply cruise in from intergalactic space ), and it can't render the whole Sovereign gambit completely meaningless. It's not that hard in theory, so I'm sure they'll manage, but ... I'm just saying, that's all. I'm just saying.
Reminds me of something I read on the BioWare forums, though. There was some speculation regarding the origin of the Reapers. Some guy was insisting they'd simply always existed. I pointed out that this is impossible, as they couldn't have existed prior to the Big Bang. His retort? The Mass Effect universe didn't start from a big bang, it just ... always existed.
I'm sure I don't have to point out how impossible this is, in so many different ways. However, if BioWare does anything like that, something that not only bends the laws of physics ( as element zero does ) but outright ignores
them, I am ... going to be very angry. For a brief time. But still.
I doubt that, though. BioWare have gotten their physics right in ways most sci-fi ignores.