What did people think of all the N7 assignments in ME2? Did they fulfill what you are after here? There were probably over 20 of them you generally only found through planet scanning, some of the requiring you to go explore planets you would have no reason to go to.
Exploration in ME2 was atrocious. Planet scanning was pain-inducing and terrible. The N7 missions that were present were generally quick and didn't provide a lot of context or story. The idea behind them, however, was not bad. ME3 did a bit of a better job making them more practical, and of course the ME3 MP continues those N7 missions. Ideally, I'd like an approach similar to Morrowind/Oblivion/Skyrim where planets are just filled with "N7 missions" in a sense.
Whether there is a base that is being held by mercs, dungeons that are filled with husks, there prothean ruins that have remnants of whats left of the Collectors, the possibilities are endless. By having these various dungeon crawling experiences in place of just fetch quests, I believe many would be satisfied. Of course completing these can raise your N7 rank over time, where you start out as a recruit and work your way up.
This would be a much more player-driven, reactive gameplay experience rather than just watching cut scenes and dialogue. I believe this is something many would appreciate as their actions would actually allow their progression in the game because of their exploration and doing the various N7 missions throughout planets. There are a lot of possibilities here.