EDIT: Haha, I forgot I already posted here!
No. In fact, looking back, we'll see it as not just fictional, but absolutely cartoonish.
However, aspects of pretty much everything is possible.
Technology? We'll likely use a lot of these tech concepts as time goes on, though not even close to the same use or extent.
Species? Very unlikely we'll see these humans in alien masks.
Mass Relay-ish transportation? Maybe. We like to think it can be a thing. But we have very little to go on.
Much of Mass Effect 'works' because of a very specific 'setup' that the Reapers put us into, and the writers allow. It is humanity breaking out into the unknown and going... oh, we were basically a small tribe that bumped into the first world. We see there's already a 'federation of planets' going on and we're the relative small fries for at least a little while.
So we have to take that as a given, and I'm not prepared to do that. Even if there are more 'enlightened federations' out there, their way of things may still not match our ways at all.
A lot of things also depend on your default standpoint for technological development:
Humanistic (flat) - None of Mass Effect is even close to what we'll see in our lifetimes, or any predictable future
Transhumanistic (increasing) - Much of Mass Effect is possible, but the context is totally off in nearly every way
Posthumanistic (exponential) - Most of Mass Effect is possible and may be at least glimpsed in our lifetimes, not that it'll actually happen
Mass Effect presents us with a 'stage'. And this 'stage' is filled with props and dialogue that all 'fits' together. We don't get challenged too much about the messiness of how things would really work, or how much work it'd take to make things happen. Mass Effect is made as the type of scifi meant to *inspire* us, but we have to know that it is based on hope, not reality. Mass Effect is NOT 'low scifi', but a whole range of low, mid, and high scifi at different points, and depending on choices and what missions you expose yourself to.
Low - What we know is possible (ME1 trending here)
Mid - What we can think is possible (ME2 trending here)
High - What we can imagine is possible (ME3 trending here)
This may be a contentious position, but I like to think of the 3 'games' as the 'Books of Shepard'. 100s of years from now, we may (or may not, but I'm just saying how it looks like how part of them are set up as) look back on them and pick and choose what was right or wrong about the games and how much was predicted of the whole fate of humanity, and what was complete fantasy.
Scifi is so often meant as an experiment in itself. It knows that we're not going to live in those stories. It knows that the context of 100s-1000s of years in the future is going to be actually unrelatible to us. But it tells the story anyway, to inspire us not just about humanity on Earth (this is more a religion thing, and something we more often see in Dragon Age), but either moving our humanity beyond Earth, or moving beyond humanity itself.
So there's going to be a tether to 'Earth' - there's going to be a lot of things we see (tech, aliens, planets, govts, etc) that either look familiar or look more possible than other things... but there's also going to be a lot of things that we just - based on the info we currently have - HOPE (or fear) will happen.
Normandy is a big example. We want it to exist. Many of us even have a part of us that needs to believe that a ship like that will exist. We really desire humanity to get to the point where space flight like that is not just possible, but widespread and encouraged. But it isn't - we're only going off the foundations of our lives here on Earth, and imagining a future that trends off of this foundation.
If Mass Effect was exclusively low scifi then I'd say that it was quite possible and realistic. However, it isn't. It goes all over the place, and acts as a tribute to all degrees of scifi that I can never say that it is going to happen in any real way. But it makes us think. It makes us want. It makes us dream. I think it is successful as scifi because of that.
And because it is that kind of scifi, Mass Effect seems to already be, and may in the future be instrumental in where we guide our science and technology in the near to mid future. Millennials, of business and of government and of science, etc, now have a segment of their population that doesn't just dream of Star Trek, but PLANS FROM Mass Effect. We (not just media, imo) call a development that heals wounds quickly, 'medigel'. We think of the Reapers with AI now. We take the concept of the Citadel from an art rendering to dream of, into an actual desired future living space that we'll want to have if (*IF*) we get to live in space this century. There was probably an increased curiosity in 'hard light', and wondering about how we'll actually practically and ethically develop and use brain implants. I could go on and on.
So yeah, Mass Effect being real isn't the point. It is about the science, and the fictions we can create from it, that propel us forward. This is one of the biggest differences between 'fantasy' genre and 'scifi' genre. Fantasy keeps us where we are, but happier about that. Scifi takes us outside, and encourages us to explore it. (IN GENERAL)