Forgetting all of the ME 3 ending fiasco, I would like ME:Next to focus more on exploration; which Bioware has confirmed they are going more in a ME 1 direction with exploration so yay
.
Apart from that, I really want to see the non-humanoid aliens take a more active role in the future titles. As NPCs not devoted solely to a running joke, squad mates with a deep and compelling backstory and rich personality, and as playable kits in MP.
Rachni, Elcor, Hanar, etc. There is so much potential with these races (IMO), they deserve more then a half second of screen time, being regulated to cannon fodder enemies to kill, and only existing to be a meme. If the next Mass Effect is going to be a 'stranger in a strange land' I can think of no better way then to break the old sic-fi trope of humans with rubber masks, and actually show aliens as aliens.
Edit: It was really sad to see all of the advantages of these non-humanoid aliens overlooked in the fight against the Reapers in ME 3.
Elcor can can carry what amounts to tank cannons into battle on their backs (how many Krogans or humans can do that?); a perfect counter to the Ravengers. Also consider how strong they are in melee combat (see being able to carry tank cannons into battle above).
But no let's just make fun of how they can't talk like us 'normals' and more or less say how worthless they are to the rest of galactic society in their fetch quest where no one even bothers to help them evacuate their home world.
Hanar are the ones that trained the Drell to be assassins, and they have actual Prothean relics on their home world (which one could assume to be in working order).
But no, let's just have a joke character as Spectre, and make fun of the fact that they look like squids/jellyfish, and we will imply that the Hanar are cowards hiding behind their planetary defenses.
Rachni are more then capable of taking down an armored vehicle such as a mako with nothing but their natural weapons, and they can breed an army faster then even the Krogan are able too, plus they are more disciplined then the Krogan as well, due to the Hive Mind mentality. And this Hive Mind mentality renders the basic drone all but immune to indoctrination; remember the Reapers only gained control of the Rachni through their Queens.
But no, let's just use them to help build the Crucible, they can't possibly help fight Reaper ground forces.