It's a funny answer - because it would work. People always claim 'Mario is too kiddy' and 'Zelda uses commic-graphic and I'll not buy', but people probably would buy the exactly same games on PS4. Because, let's be serious, which games set PS4 apart from the competition? Right, no ones, most stuff is also available on PS3 or PC or X1. Still people buy PS4 for these games, not too few buy again games as remasters, they played a year ago on another console. So it is nothing about the games, it is all about the image. That's why Nintendo-consoles are unacceptable for the west, and nothing Nintendo does in the short term will change that.

I'm not making it up, a person from Capcom even said their goal was to attract the COD crowd.

It was risky, but they kept it in the same genre and appeased their fans when they made the transition. You are hoping to turn Metroid from an action-adventure to an action game. A good multiplayer doesn't necessarily have to detract from the single player, my issue is if they focused on multiplayer (as they had in the past) and the single player was of poor quality (Metroid Prime Hunters.) The only other example of multiplayer was Prime 2, and that multiplayer wasn't that great. I'm speaking within the context of Nintendo's limitations. If they can pull of a Metroid game with good multiplayer without taking from the single player, I'd love that. An example of a series like Metroid is Bioshock. I consider both games to be in the action-adventure genre, and much like how multiplayer detracted from the single player in Hunters, so did multiplayer detract from the single player in Bioshock, the difference is Hunters multiplayer was actually fantastic, while Bioshock 2's wasn't that great (in my opinion.) Bioshock and Metroid Prime also have similar story-telling methods (albeit Bioshock is more cinematic.) 

The western Nintendo-gamers bought Bravely Default and Monster Hunter Tri sold pretty good in the west (>600K in the US and 400K in europe). This with near to no western advertisement. Youkai Watch isn't released in the West yet, but if we look at Pokemon we can safely conclude it will be as popular in the west as in japan. So western nintendo-gamers obviously like japanse-oriented games (something the PS2-gamer also liked, but obviously not the PS4-gamer).

As to violent- Bayonetta is well received in the west, as good as the first on PS3 and X360. So I don't see Nintendo-gamers shy away from violence. I don't surely know what you mean with level of realism, as GT and The Sims are both unrealistic games in a sense. You should elaborate this more.

When did I say that? Also, Metroid was always a side scroller shooter/action since NES days. What's not an adventure game anyway in the shooter realm?

Bioshock has a good story development but it's an average FPS. If Nintendo fans want that, oh well.

Halo is an action game. You want the game to be like Halo. The difference between an action-adventure and an action game are features like linearity, and backtracking. Halo is far more sequential and linear than Metroid Prime and Bioshock, and that's why it lends itself to a cinematic storyline. Metroid Prime and Bioshock let you find the story in any order you choose, and even let you ignore parts of the story if you wish to. For example, in Metroid Prime 3 Corruption, there is a backstory to the planet Bryyo that is very interesting and you can only find out about it after reading scans. In Halo much of the storyline is told through cutscenes or the canon-based novels. In Bioshock you have recordings and messages that tell you individual backstories relevent to Rapture as well as cinematic cutscenes. 

As for gameplay, I find Bioshock to be the more appealing game (compared with Halo 1-3: the ones I played fully) regardless of shooting mechanics. Not only is the cutomizability of plasmids a breath of fresh air, but the adventure aspects and lessened linearity are much more appealing to me. The world also is more immersive and atmospheric for me than Halo ever really was (not to say Halo doesn't have any of its own immersion.) Metroid is primarily an adventure game and a shooter secondarily. This has been true since at the very least Super Metroid. You had action side-scrolling shooters like Contra, and you had action-adventure ones like Metroid, just like today you have action- FPS like Halo/Killzone/Resistance/Millitary Shooter #9000 and Action-Adventures like Metroid Prime and Bioshock. Some games blur the line of course, but nevertheless these distinctions can still be made. 

Metroid Prime Hunters was billed as an MP game anyway so it makes sense the SP would suck. Bioshock 2? it didnt detract from the SP. That is a fact. the MP aspect was made by a completly different dev team in a different country so how could it detract from SP when they had no interaction? Uncharted that is a series that got both right. IT can be done now whether Ninty has the SKILL to do it...maybe maybe not.

Even if  time wasn't spent on BIoshock's multiplayer, money certainly was. Hell, the game had like 7 different teams working on it, all with different salaries, and different costs to maintain.  Money is just as much of a constraint as  time in video game development.