I would really like a similar mechanic for Mass Effect. I was never a fan of thermal clips, nor the forced attempt at an in-game explanation for a purely gameplay decision. The thermal clips were added to make ME2 play more like traditional shooters, and thus make it more widely appealing. Maybe this change (and others) worked as intended, since ME is now a widely recognized AAA IP.
That's a gross oversimplification.
For one thing, thermal clips were not added just "to make ME2 play more like a traditional shooter." Mass Effect 2 wan't designed by a marketing department. The clips were added to speed up combat as well as potentially encourage all the things I mentioned earlier. Had BioWare committed to the mechanic, thermal clips could have added another vector of depth to the combat.
Second, there's a reason more traditional mechanics are more appealing: they're fun. BioWare replaced a clunky mechanic with a better one. That's good game development. Yes, there were probably ways to achieve more lore-friendly ammo mechanics, but BioWare's decision to have an ammo mechanic doesn't make them sellouts.
Overwatch shows an up-to-date, fun mechanic that would allow for the logic of ME1's intrinsic heat sinks, as well as the satisfaction some get from actually "reloading" a weapon, as with ME2 and ME3's thermal clip/ammo mechanic. Best of both worlds, in my opinion. I think this would be my preferred method, of the three approaches (ME1/ME2-3/Overwatch).
Overwatch doesn't show that at all. The mechanics of a multiplayer arena shooter don't automatically translate to an RPG/TPS. These two genres have completely different design objectives. You don't need to have ammo reserves in Overwatch because your average life span wouldn't be long enough to burn through all those stores anyway. There's no reason to encourage weapon swapping because you can't actually swap weapons (save for certain characters with specific powers), nor is there any reason to encourage exploration because you fight in small arenas and have a singular objective. Power usage is encouraged because there's no way you'll survive on bullets alone.
Mass Effect, however, could have extended campaigns through enemy territory. Ammo scarcity, though somewhat out of place in lore, makes perfect sense within the game mechanics.
I suppose Overwatch could stand as proof that not all shooters need ammo, but that was never in question. Good game designers don't haphazardly grab mechanics from other games just because they work in that specific environment. They must consider what design objectives that mechanic fulfills in the other game and determine how well those objectives fit into their own game.
I suppose Overwatch stands as proof that not all shooters need ammo, but that was never in question.