Sony doesn't have anything worth moving to the 3DS. Nintendo is in a trickier situation as they have valuable console games that wouldn't work on a handheld. They aren't equivalent situations.

It'd be better for gamers if Nintendo started making Vita games. 3DS isn't capable of running Little Big Planet without massive compromises to the actual game design. It uses multi touch which 3DS doesn't have.

You'd also have to cut back the scope of level design due to lack of processing power.

There is nearly a generational leap between the 3DS and Vita and it would only negatively impact on the end product if compromises were made to port games from Vita to 3DS.

Add in that games like KillZone would tank harder on 3DS than they did on Vita and going 3rd party for anything other than jak and daxter would be commercial suicide. It would also mean Tearaway would not be possible until next handheld gen or would have been an iOS game.

Sony always try to make developers happy as much they can to create their games quickly and risk free. They failed in PS3 by giving an odd architecture to program but the hardware is powerful. Now, they have provided powerful hardware and also easy to code in Vita and PS4. So, future of Sony is bright and they don't need to release their innovations in 3DS because they can earn more profits by releasing Tearway in PS4/PS3(mostly it will come) intead of 3DS.

Also i expect Tearaway to do well in PS Vita in long run, its just that these holidays people have been spending so much on next gen and many others so they did not give attention this game. But, i'm sure it will do great in the long run because always hardwork will get payed off but it might take some time. 

Am I the only one here who thinks that Microsoft is the one that would benefit most from going third-party?

I don't think Microsoft would benefit at all from going third-party.

Even after not making much profit off of its game division in the past decade? If it weren't for Sony's PS3 missteps, I don't think we'd be having this conversation.

I don't want it to happen because:

1 - it doesn't have a second analog stick (KZ cited on the OP would totally suck on the 3DS)

2 - Nintendo's online multiplayer usually sucks

3 - Not as indie friendly as the PSN Store

4 - No OLED screen

5 - I would rather play those games on PS4 then on 3DS, most of the games give us the console experience, I don't think 3DS can deliver it.

6 - I don't want live in a world with no dedicated handheld gaming competition, if there's no competition they will get lazy and develop us mostly cheap stuf

The OP is kind of weak, and it has been used before. But some of the replies are just pure gold. This thread deserves a 10/10.

Sony has their own 2DS-handheld with a much larger installbase: the PSP

So if they really wanted to develop further handheld games with a resolution around 400x240 / 480x272 and only one analog stick, they could stay on their own platform... these games would even be Vita-compatible. ;)

Gameboy, GBC, and Gameboy Advance would like to have a word with you :P