I may have posted this elsewhere, the topic was "what do you want to see in ME4 (Andromeda) class-wise?" but for the life of me I can't find it, so I'll put it here.
One thing I like to do in ME2 and ME3 is use the Gibbed save editor to switch classes, (my headcanon is that my Shepard is a Vanguard/Sentinel hybrid, but that's another thread)
So to implement that idea into actual gameplay, it would involve something of a hybrid between the resource collecting from ME2 and requisitions from DA:I.
I'll use the classes/powers from ME3 for simplicity
Example:
You are a Vanguard (biotic/combat) and you want to switch to Soldier (full combat), alright, you'll need 20 weapon fragments, 2 ammunition blocks, and a Disruptor ammo designator.
Or Engineer, you'll need 20 components, omni-tool processor, and a V.I. interface
Or Sentinel, 10 components, omni-tool processor, and 50 units of eezo
Etc. etc.
The idea is that like the Medbay where you could reset your powers at a cost, you could use resources in the field to alter your abilities to suit the situation.
It would also provide ready materials for a crafting system, weapon fragments from defeated enemies, ammo blocks from an abandoned weapon cache, components from defeated synthetics, etc.
It wouldn't be something that you could just switch classes just for kicks; it would be an investment, something that you would have to go and gather the materials or visit a shop. You would have to consciously make the effort, but you wouldn't need to sell half the ship just to Incendiary Ammo
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The other idea I thought of was a point-buy or tier hybrid, where you answer a few questions regarding playstyle and the game "creates" a class for you, which you can then modify as you see fit. Something like Biotic Charge or Tech Armor would be expensive, to the point where you could only really pick one, but a power like Pull, Throw, Cryo Blast, Overload and the like would be relatively cheap.
Or maybe a simple "fill the slot" system, like the Vanguard: 1 class power(Charge), 2 "main" powers(Nova, Incendiary Ammo), 3 "supporting" powers(Cryo Ammo, Shockwave, Pull) 1 passive(Assault Mastery) and Fitness.
You could go with the "standard" classes or make your own.
Another bit would be picking a "class power", and then building your class around that power.
I have 100 points to spend:
Say I pick Tech Armor, and I want to plant myself in the middle of the battlefield as a line in the sand. I pick Sentry Turret as the "line" for 20 points, and then Shockwave to push enemies back for 10. Since I'm gonna be in the middle of the firefight, I need more firepower, so I pick Incendiary Ammo for the remaining 20 points.
The idea is that your class power sets the "tone" of your class, and the various other powers would be more/less expensive based on type proximity, i.e. a Biotic class would be able to get Warp for 15 points but a Tech or Combat class would have to spend 20.
TL;DR
Build-a-Bear meets Subway meets Mass Effect ("Mass Effect, biotic fresh!") Pick from classic options or create your own!
Now in 3 different colors and 5 scents including Tides of Thessia; Clean, Crisp, Citadel; and Tuchanka Sunshine *Warning: Tuchanka Sunshine may cause burning, chest hair, sudden emphasis and exclamation of "I. AM. KROGAN!", thresher maws, death, and mild itching. Discontinue use if you feel fatigue, nausea, and/or irrational desire for fish. Unless you're Commander Shepard, in which case please stop dancing.
MAJOR EDIT:
I thought it was single player, I missed the "MP" after "MEA" in "MEAMP"
I suppose it could work for multiplayer, but was thinking of single player. Apologies.