If it sells more then the 3DS it would be a great success story.
If it sells around the numbers of 3DS it would be a success.
If it sells between the WiiU and 3DS numbers it would not be a success but can count on a long support.
If it sells around the WiiU numbers it would be a disaster and could meen the end of hardware from nintendo.
If it sells less then the WiiU this will be the last console by nintendo

They won't lose on the hardware but what about software and R&D costs? Just selling hardware won't make them a profit.

Not true, they need to make back R&D before they can turn a profit on the console

I'm sure Nintendo will be happy with 50-60m, the shrinking numbers in hardware will be compensated by the growing software sales a hybrid market will provide.

For me? Enough to keep the lights on and making games.

Enough for them to make a good profit.

50 million would be decent.

No, Nintendo has a hard time supporting two seperate platforms and this problem continues to grow as games take longer and cost more money to make.

If Nintendo released a $200-250 PS3/360 level handheld alongside a $300-350 PS4/XBO level console than Nintendo will have to make games for two distinct platforms and consumers will have to spend $500-600 to have access to the full Nintendo library.

By offering a single $250-300 device that is about halfway between PS3/360 & PS4/XBO and acts as both a handheld & console, Nintendo can increase their output while consumers need to spend half the money to get full access to the Nintendo ecosystem.

what if their hardware sales decline but software sales increase? would that be considered declining in relevance?

Anything under 75 million is a big failure. But they should be able to clear it easily.