A continuation of some ideas, features, and concepts I would like to see in the next Mass Effect game.
The protagonist should not be Shepard 2.0, as in a legendary, impossibly heroic, somewhat high-ranking commissioned officer who can somehow completely avoid military bureaucracy to achieve his/her goals, save the galaxy multiple times along the way, and 'enkindle' multiple willing members of the opposite (or same) gender along for the ride.
That being said, I would like to see a system like that of Dragon Age: Origins, in which the protagonist's background has some influence on his/her starting point, selectable class, and story arc. For the sake of simplicity, the starting location for the protagonist, regardless of background, should be the same, but the way the events unfold would vary based on the player character's (PC) background. It would be nice to be able to play as a non-human, but the species choices would have to be limited to the most humanoid races (i.e. asari and drell).
For example, if the selectable backgrounds were Mercenary, Intelligence (as in civilian intel organisations like MI5 or the CIA), Military, or Spacer (i.e. a rogue trader, Han Solo-esque character), the starting point for all the characters would be a facility similar to Lazarus Station. The story could start with the interrogation of a prisoner, with the Spacer and Mercenary PCs being the prisoner, and the other two origins serving in the interrogation role. Something would go awry, and the protagonist would have to deal with the immediate opposition, and escape the space station.
Class and species selection would be directly related to origin choice, one way or another. Humans would be able to select any origin, with their class limited by background. Asari players would be limited to Intelligence or Military backgrounds, and drell to Spacer or Mercenary. Assuming a human protagonist, the class selection (using the 6 classes in the ME trilogy) would be as such:
Mercenary: Soldier, Infiltrator, Adept
Intelligence: Infiltrator, Engineer, Sentinel
Military: Soldier, Vanguard, Engineer
Spacer: Engineer, Sentinel, Adept
(The above is purely for illustration, and not my final thoughts on how I would like to see the class/origin restriction, if any, delineated).
Species, background, and class would all play a role in interactions with NPCs and acquisition of morality points, with certain backgrounds facilitating Paragon or Renegade point gain. Gender, appearance (facial features, skin tone, hair) would be customisable where appropriate, with asari limited to female gender, and drell having no hair to customise.
In fine, the features I would like to see incorporated from other games: Dragon Age: Origins--varying backgrounds, species/race All Mass Effect games: player customisation, fully voiced protagonist, class selection with appropriate powers.
~Prior History and Old Friends~
All endings of ME3, with the exception of the 'Refusal' ending, can be incorporated. Regardless of the ending, the player would come across references to the Normandy crew and the ship herself, perhaps in the form of memorials, or even encounters with crewmates from all three games who could possibly still be living a century after the end of ME3 (if they survived through the end). Namely Liara, EDI, and perhaps Wrex and Grunt, although in the latter case, his tank-bred nature may result in a shorter lifespan than normal krogan. Shepard could be encountered only if the Control ending was selected.
Synthesis, the most troublesome ending to incorporate in my opinion (and also my least favourite), could be shown by the green subdermal circuitry that all species apparently have, as well as more accepting views of AI, and the presence of benign Reaper vessels. The protagonist would encounter Geth that seem far less strange and inhuman than Legion and his brethren in ME2 and 3, and perhaps even have a mission in which he/she meets EDI. The Normandy herself would be featured in a museum or memorial, with appropriate memorials in cemeteries for the heroes who served on that vessel. The player would also be able to meet Liara at some point, and hear first hand about Commander Shepard. Dialogue would differ based on whether Liara was romanced or not. Shepard himself/herself would have a monument on Earth illuminated by a green eternal flame, with the grave of his/her love interest next to it (assuming that it wasn't Liara).
Control would be similar to Synthesis, in that friendly Geth are present, and that the player can meet EDI and Liara, but without everyone evincing subdermal circuitry. Reaper vessels would also be present. In this scenario, however, the player would have an opportunity to meet Shepard, who is now in Reaper form, and as esoteric and inscrutable as Sovereign, but not malignant. Shepard would not have a grave site in this scenario.
Destroy would not feature the Geth or EDI. However, the player could encounter 'proto-Geth,' created by a new generation of Quarians, that would resemble the original synthetics, but with safeguards taken to avoid another Morning War (i.e. these AI are created as individuals, not as networked intelligence, and are treated as equals, not servants). The PC would be able to meet and talk with Liara, visit the Normandy memorial, and find Shepard's cenotaph on Earth, with his/her love interest (other than Liara) interred next to him/her.
Galactic history of other events would be related through NPC dialogue, codex entries, and player experience. As we saw in ME3 with Legion, it is possible for the player to see past events firsthand. Choices made throughout ME3 would play a role in which species are present or absent--if one sabotaged the Genophage cure, there would be no krogan; Destroying the Reapers would mean no Geth (though early prototypes of new Geth could be encountered), choosing the Geth over the Quarians would mean that none of the latter would be encountered, and Rannoch would look different.
In fine, one's choices in ME3 would play a notable role in the next game. Missing persons or individuals would not have placeholders; rather, these flashbacks would be optional sidequests whose availability and content would be dependent on the imported save.
I like the Paragon/Renegade system with interrupts, and the Reputation system of ME3. However, it would be nice if the Paragon/Renegade choices were not colour-coded, or dependent on accrued points. Rather, the moral choice should be left up to the player to decide, and the points received would be part of the consequence. As I mentioned in part I, armour/attire, as well as one's class, background, and species should play a role in how NPCs react to the player. Paragon/Renegade points would determine side missions received, and key choices (outside of dialogue) available.
A brief outline of a potential plot, and a few more points in part III.