There's no option to roleplay in MP. The "playing as an alien" was playing as a human with a different skin.
The roleplaying is limited (at least in ME3, who knows what they are doing for Andromeda) but it was definitely not the same playing as a human with a different skin. I don't think a lot of people appreciate just how much the gameplay changes with a different alien for a base.
You have different health and shield values, different dodges, different melee abilities, different damge multipliers, different movement speeds, what classes you can pick and what powers are available, special powers like rage, regeneration, not being able to take cover etc.
Now in general...
People are making the argument that it is a waste of resources, but there is very little that can give such a large and positive amount of gameplay variety as introducing more playable species, especially when they already have to add all the animations and design for multiplayer.
Given that we spent the last 3 games playing a human orientated a story I think it was time to branch out and do something different. Yes, their is more work to add to the story to make it as immersive as it can be, but I would personally prefer that work to be done over a huge number of other things.