I love my N3ds. Clearly it has worked for Nintendo (so far) in at least temporarily boosting 3ds hw globally. But why would Nintendo release something to just temporarily boost something? It cost money to develop new pieces of technology (they had to rellocate/redesign the whole thing to make it fit and work) and I seriously can't see them doing it just to increase a few months of sales (that would be a waste of money spent in development). Here is my thought:

Nintendo may be planning to push N3ds for the next 5 years as their cheaper device that you can play Ds/3ds/N3ds games on and they may be planning to release a whole bunch of Wii remakes that require the N3ds model. They may do this all the while releasing the Fusion device that can play the next Nintendo hardware games on the go (in decreased resolution/graphics) but costs a good deal amount more. Basically, I think the N3ds will be the thing that keeps Nintendo profiting while the rest of us wait to buy into a device that is sure to cost a lot up front (the fusion handheld). It's a way of maintaining profits (with N3ds surging with Wii remakes) while they increase their userbase on the Fusion handheld to the point that it becomes profitable. This is my latest prediction. What are your thoughts?

N3DS was a measure put in place so that they could extend the life of 3DS hardware/software sales until their next-gen platform is ready.

Probably not, u asked why would Nintendo release a revision if they are planning on replacing it in 2 years, well that's what Nintendo always does.

Gameboy Advance released about 2.5 years after Gameboy Color, Nintendo DS released less than 2 years after Gameboy Advance SP, Nintendo 3DS released about 2 years after Nintendo DSi and the next handheld will release about 2 years after New Nintendo 3DS.

the question now would be in 2 years can we see a fusion console from Nintendo. Replacing both Wii U and N3Ds?
better hardware specs for both handheld and home console versions of the Fusion?

I'm sure the developement of the N3DS was not that expensive, the only aspect that really looks that way is the new 3D effect and the Amiibo reading screen. Nintendo will try to keep the 3DS alive as long as they can, so they can develope the Fusion idea as well as they can (at least that's what I would like).

It's not the first time they have a HW revision on their HW with inner changes aswell.
And it's not just that, if they can't support 2 consoles with sufficient content, developing games for the N3DS, fusion consoles and QoL, in a meaningful way, would be almost impossible.

More than ever, they need to allocate their resources to replace the absent 3rd parties and have diversity in their library.

It's a stop gap. Nothing more to it.

For nintendo to push the "fusion", the fusion has to exist.

Similar to Gameboy Color, Gameboy Advance SP, Nintendo DSi, all revisions with noticable upgrades that were replaced about 2 years later.

The n3DS is released only to increase hardware sales..

Look at the Gameboy Color, Advance SP, DSi, XL models, Wii Mini, etc.

This is nothing new, as they have done this a lot.