I just remember something that the DA team said about something similar in regards to the human-centric stories. It was something like, "Well, we're human and it's easiest to write for a human." ME has been known for having a human character with some options to tweak personality, looks and playstyle.
I also enjoy it, because it's a good player avatar. Someone from the outside to ask questions that are obvious to everyone else. Unlike, say, FFXIII, where everyone talked to each other like they knew what they were talking about, and the player has to scour the massive Codex to figure out what's going on.
I'm not opposed to the idea, at all. However, I prefer human-only for ME:A. This allows us to learn more about the new galaxy and possible new races while avoiding things like, "Who was Mythal?" as an elven player. (DA:I) I'll admit, I like being a human hero out saving the galaxy. Unlike DA, ME takes place in more or less our future, and I like being a human hero saving the day in my "what-if" future.
I want DA to keep multiple races, because I feel it works much more there, and I don't think a set PC would have made a difference in the End Product. I think DA:I's problem is that someone wanted to cram every idea in their head for exploration and quest variety to where parts of it came out pretty incoherent and jumbled. Also, spreading themselves too thin in general.
Plus, DA only had 3 other races to choose from besides human. That's pretty much all there is for civilized races in Thedas, for the most part. With ME, you have: Turian, Quarian, Bartarian, Human, Drell, Hanar, Volas and more, including any new races that ME:A might introduce. That would make it way too hard to keep a somewhat unique story for the PC. Meaning that if you thought race reaction in DA:I was bad, I think it would be a non-existent in ME.
Nah, let's keep it human only for the Mass Effect series. It'll produce a much more tightly focused story, and I think a richer experience overall.
<avoiding the latest set PC vs custom PC debate in relation to TW>