How Can Bioware Add New Races to the Story?

Get out of the Heleus Cluster to other star clusters in Andromeda, which I think will be a possibility in future games based on the discovery of Remanent technology.

We know the kett have enough resources to travel cluster to cluster. There is also the Jardan technology. It might be possible for easier travel in the future.

I'm thinking that a future game will entail pursuing the Kett. I imagine finding races along the way who have been largely decimated by the Kett and willing to fight them til the bitter end. After all, defeating the Kett would mean they could survive and thrive again. So we got two new races openly revealed in MEA, as well as reference to the Jardaan. I figure the Jardaan will show up along the way, unless they're planning to make them the MW "Protheans" in the sense that they're long dead. Hope not, though. Maybe in MEA2 we get to meet the Jardaan and perhaps another race. Finally, MEA3 could introduce a couple more for the final battle against the Kett. There's potential for up to six new races to be introduced across the series without overdoing it in any single game.

You know, i really get the impression that the Jardaan aren't some benevolent race.

The whole Angara creation feels to me like they were trying to make some "shock troopers" who would be able to interact and use their technology. But why do that?

Then there is also the vaults. The Ryders can learn how to interact with the them to reset the vault and fix some of the damage caused by the Scourge. But during the course of the game we learn they (vaults) were there before the Scourge happened so their primary objective wasn't to heal the damage to those planets. So why terraform garden worlds?

I know there isn't any hard evidence but i get the feeling the Jardaan are as big a menace as the Kett.

It's science fiction, the possibilities to introduce more aliens are endless.

A simple one, refugees driven out of their home cluster by the kett arrive in heleus. 

I actually hope the Jaardan are at least somewhat benevolent. I don't need them to be perfect angels, but I'd like for them to be a largely benign society, perhaps driven into obscurity by whatever unleashed the scourge. One of the things I really like about the remnant, the vaults, the reveal about the angara and Meridian is that we finally get to have some ancient technological wonders that aren't Ancient Evil, like the space blight we got in the trilogy. All of the things we use in the Milky Way are basically part of a huge death trap. I hope that's not the case here.