Padzi
Liturgist
I think a more interesting choice would be a trilogy featuring the discovery of the ruins in Mars, the relay at the edge of the solar system, the subsequent exploration, first contact war and integration into citadel space.
In my opinion this would be the best choise for a sequel/prequel. You don't even need to invent some new weird plot like they had to with Prospermeda. The basis of everything is in the game's codex and it deeply rooted in the established lore. Every half-decent writer could hande this. But I don't think there is enough material for making a trilogy out of this. Although one game taking place during the First Contact War would be a great idea. (When they annouced ME4 I hoped it would be set during this time period).
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And they are still trying to revive Andromeda's corpse. Too little, too late:
Though I am intrigued by what are they planning to add. And what is his favourite change.
You know for science to better understand a developer's mind.