Mac Walters on the Star Child/Reapers
"Originally, with the catalyst, the star child at the end of the game, I had written that much more in the guise of a investigative style conversation, where there is something he tells you but then, you get to ask a bunch of questions and you get your questions answered. But then me and Casey talked and decided, lets keep the conversation "High level". Give you the details that you need to know, but don't get into the stuff that you don't need to know. Like "How long have they been reaping?" You don't need to know the answers to the mass effect universe. So we intentionally left those out"

Casey on after Mass Effect 3
"Whatever we do would likely happen before or during the events of Mass Effect 3, not after"

On delaying the game
In march 2011, he also faced a room ful of Mass Effect developers who expressed concern about hitting the promised holiday release date... New release date set for March 2012. After much deliberation, the CAT mission (or rather, the Prothean mission) had to be removed from the set of tasks. The missions would later be completed as post-release content"

Casey on the End Boss
'We had the final fight with the Illusive man in the game, but it just felt very Video Gamey. It didnt fit in with the themes. And really, is there a point of the end boss if only for the sake of an end boss?'

The article also states 'Although art was created for this sequence, it was ultimately dropped because it felt too predictable to end the series on a massive boss battle.'

On Tali's Face
We eventually decided that she gives you a memento of her pictures, but the team was throwing around a lot of pictures and designs until we decided on something and said "Yup, that's her".

On Deciding the End of the Game
The illusive man boss fight had been scrapped... but there was still much debate. 'One night walters scribbled down some thought on various ways the game could end with the line "Lots of speculation for Everyone!" at the bottom of the page.'

In truth the final bits of dialogue were debated right up until the end of 2011. Martin sheen's voice-over session for the illusive man, originally scheduled for August, was delayed until mid-November so the writers would have more time to finesse the ending.

And even in November the gameplay team was still experimenting with an endgame sequence where players would suddenly lose control of Shepard's movement and fall under full reaper control. (This sequence was dropped because the gaemplay mechanic proved too trouble some to implement alongside dialogue choices).