The good thing about trilogies is that across the three games the writers get a lot more game hours to develop characters and more opportunities to get the players invested in their stories, or their relationships to the protagonist. That isn't to say that the next game needs to be the start of another trilogy, but there are some benefits to a multi-game series with a returning cast that plays to Bioware's strengths.
See, this is where I think we will have to temper our expectations a bit in regards to MEA. Since we'll obviously be comparing MEA to the original ME trilogy, we have to keep the following in mind as well:
Mass Effect Trilogy had 3 games and a bunch of DLCs dedicated to the universe, characters, etc. You literally spent 150+ hours with the same cast, with evolving circumstances, jumps in timeframe, new events unfolding. These different conditions and circumstances allowed our favorite characters to evolve, and let us get more attached to them. Just look at how Liara evolved. She went from shy scientist, to information broker, to gushing over an actual Prothean. We got to see her in different situations over multiple games, allowing us to get attached to her more.
In MEA, we will most likely have one single standalone game. Say we have a Turian squadmate. This Turian squadmate will not have the same depth of character and backstory of Garrus. That's unreasonable to expect. MEA will have this Turian squadmate for 1 game, vs 3 for Garrus, not to mention we get to see Garrus go through a big evolution from ME1 to ME2, thanks to Shepard's encouragement.
Unless MEA has triple the content of a single original Mass Effect game in terms of character development, loyalty missions, dialogue, etc., we will not get attached to these squadmates as much as the ones in the original trilogy. That is, unless we get even higher quality character development then we're accustomed too.
Just hopping that everyone doesn't start setting expectations for Garrus Dudebro 2.0 (though that would be awesome if they managed to do it
)