Sure it's possible.  It may happen every once-in-a-while, though we certainly haven't seen it yet.  Halo sacrificed Single Player for Multiplayer.  Gears did the same.  The last game I can think of that didn't was Goldeneye back on the N64. 

Here are my thoughts;  you can split development into single and multiplayer, and with Retro's talent have a great single player and a great multiplayer.

OR

You can only focus on single player and instead of it being great, have it PERFECT.  That's what I want.  I'm not interested in it for multiplayer.  If it had it would I play it?  Yeah, I would mess with it some.  Would that matter to me at all? No.  There are plenty of multiplayer shooters.  What the industry is LACKING are deep, engaging, and challenging single player adventure experiences.

truth be told?. NOne.. ^_^ ' but that doesnt make my point any less valid does it?. never had a gamecube and i just move to the US trying to learn the English language.. so sorry in advance if i might sound rude or just start rambling some incomprehensible language >.<...

preordered it though, since im really intrested, i also looked up the story and stuff, how metroid prime isnt really a sequel of the metroid series it sort of in the middle.. how she was raised by owl people and stuff..

To expand even more, in my opinion criticizing Metroid Prime 3 for no multi-player is like criticizing Bioshock for not multi-player. That's not what the games are about.

That's what I thought, and yes, it makes your point less valid. If you have not played Metroid Prime, then you do not understand why multiplayer just isn't appropriate in this game. If you're expecting a first person shooter, you really need to look elsewhere. Metroid Prime is a lot more like Super Metroid (a 2D action-adventure game) than Halo.

EDIT: Well said, naznatips.

EDIT 2: Let me put it a different way.  If your argument is that the Wii could really use a game more like Halo, and that it would attract more new gamers to the system than MP3, I agree.  The Wii needs a really fun multiplayer FPS.  But Metroid Prime 3 is never going to be that game, and Retro shouldn't try to make it that game.  You saying that MP3 should have online multiplayer is like me saying Halo 3 should have more exploration, searching for combat suit powerups, big boss battles, Ridley, and Metroids.  Those are all great game features, but they don't belong in Halo 3.  Those features are what makes a Metroid game.

"you sound like the devs are bound to fail if they added multiplayer... again in my previos post having good polished single and multiplayer mode is possible.. i understand that it would take a lot more effort but im sure they can pull it off.. have you played MGS 3, though not a very good example cause its multiplayer mode isnt that good, but its single player mode is polished as hell!. that way the game caters to the old metroid fans and gain new ones..

 "bringing multiplayer would attract some people" ?. if its great like 100's or 95's in review scores cause of its controls and multiplayer, you think it will only attract some people?. i think it will attract a LOT of people, even "fps nerds" that are so used to the mouse if they heard the wiimote is a lot better would buy wiis, not like wii sales needed more moving, but still, i bet it would attract a lot of people.. "

how can that be less valid?. even if i havent played MP, i still think its valid..

 and naznatips im not trying to put down the game, i know it can hold its own with just single player, but wouldnt multiplayer be great?.

and this might sound something coming out from from "LA  LA" land or something but what about a "perfect" single mode with great multiplayer.. devs might surprise you..

 but like i said im really interested with MP3, and reading about how its wii's biggest chance to capture the fps genre, i think multiplyer could really help it.. and retro was thinking about multiplayer which meant it was probable before..

and what other multiplayer fps with wiimote controls  game?.

So tell me - who here owns Metroid Prime 2: Echoes - and regularly plays/played the multiplayer portion of the game?

I might have put 40-50 hours into MP2, and never - not even once - even tried the multiplayer. Its not that it wasn't fun/good, its just not what Metroid is about. 

...

Once Retro have this out of the way, I'd be happy for them to work on a online, multiplayer, sci-fi shooter (new franchise?) for the Wii. Hell, they could even do a Metroid spin-off ;)

 Well that multiplayer was truly dull.

We're talking about if Retro actually took the time and made a good, solid, multiplayer mode.  I'd at least play that a few times, I'm sure many people would.

Man...a Metroid spin-off would be cool too.

In MP3, apparently the Hunters are back, but helping you?  Various bounty hunters on your side now?  All those characters could be included in a multiplayer mode if Retro took the time.

good point ='(.. but still games evolve.. so hopes always there (hope for me atleast)..

btw i never played Halo, i was a counter-strike fan though..

and its not like multiplayer needs to have the samme mechanics as single player..

i remember playing a game, i think it was future cop, when i was small, multiplayer was really fun though completely different from the single player experience..

No, you don't understand.  It's hard to get you to understand when you haven't played it.  I never thought you were trying to put down the game, I just understand that you really have no clue what kind of game you are trying to force a multiplayer into.  The place I highlighted is where you go wrong.  That's where your entire argument goes way off in the distance.  Metroid Prime 3 is NOT AN FPS.  Metroid is a First Person Adventure.  Yes, the primary form of combat is guns, but it's an adventure game not a shooting game.  Metroid is no more an FPS than Resident Evil 4 is just a 3rd person shooter.  You don't understand the game, so you are really arguing that a game you don't know much about should have a feature that isn't good for it's style of play.

As far as better options:  Red Steel 2 should have online multiplayer.  No, Red Steel wasn't good, but it was a rushed release title.  A from the ground up shooter for the Wii built with time and money with good controls is what the Wii needs for online play.  METROID IS NOT THAT GAME.  I really am tired of trying to explain this to someone who hasn't played the games before, because they don't understand.

Shams, I turned on MP2's multiplayer once and never touched it again.  I have beaten the single player 3 times 100% completion though.

I think its easier to explain by saying this:

Metroid Prime, without multiplayer = AWESOME

Metroid Prime 2, with multiplayer = NOT SO AWESOME

And the screens are just impressive.