Very hard. But please, be my guest in presenting a reasoning to support that number.

So far, you've only talked about:

1 - The system has sold 7.1M in 5 months. But you must take into account that among those 5 months there is the launch period and the Christmas season. Considering only this year, April is the 4th month and PS4 is at 2.7M. By the end of the month, PS4 will most probably be at 3M in 4 months. That doesn't sound as good, does it?

2 - A 10-year life-cycle. But you must take into account that the 8th, 9th and 10th years won't be as good.

3 - New markets. China hasn't got 1.3B people overnight. That country, as well as India, Brazil, Russia, Indonesia and many others had already hundreds of millions of people during the 7th generation of videogame consoles. But there's a good reason of why only some thousands have bought consoles. And that reason will not evaporate now on the 8th generation.

Basically what I came here to say.

Wii is the only reason last gen was overall so strong. Without that power this gen, there's no way the console market will do better than the last two gens. Additionally, PS4 can't pull a Wii without hurting Xbox One. So, if PS4 does pull a Wii, Xbox One is screwed and Wii U will do whatever it was going to do leaving one super strong sales console and two not so amazing sales consoles. PS4's success could be a double edge sword. 

Just to add to this.

I'm from Brazil, and i can tell that most of us here buy imported from USA (at least in the first years of every gen). So a good part of our numbers are already on charts. I imagine the same goes for other countrys in LATAM, and maybe China (towards South Corea/Japan Charts).

Mobile gaming is putting a dent in console sales, but when some of these android consoles start selling, like Google's upcoming console, it will steal even more sales bc even a cheap console is an effective substitute for a full blown console, the big 3.

It is in decline from last generation, which will end up being the peak of home and handheld consoles. We know for a fact that the Wii U, Vita, and 3DS won't outsell their predecessor. The PS4 will likely outsell PS3, but that's not certain, and the One has a chance of selling the 360, but that also might not happen. So 1/5 or 2/5 outselling the last generation is a definite decline. The truth is that tablets/smartphones have eaten up the handheld industry and they affect the home console industry as well.

Yep, but it's only MS and Ninty to better their consoles situation, so it would be reasonable to expect them to do it. With XBOne and Wii U in a good shape, 8th gen has some chances to become slightly bigger than 7th.

the only chance the new gen has of increasing is if the mobile market starts to die off, which is not looking likely. Also take into account that many children are using tablets instead of dedicated gaming devices, the future is starting to look bleak for gaming.

In addition to my previous post on PS4 and XBO, I would like to move on to the handhelds. All that is required of 3DS and PS Vita to outsell there predecessors is cellular service. Really, it is that simple. If Sony and Nintendo would step up and deliver what people want, they would be greatly rewarded, but until they add a cellular capable model to those devices they will continue to loose market share.

So, basically, the way I see it is, it is up to Sony, Microsoft, and Nintendo were this generation goes. If Sony and MS continue to push amazing games, and put up a serious fight against the cable and satellite providers, then PS4 and XBO will easily sell more the PS3/360/Wii. If Sony and Nintendo drop a cellular capable 3DS and Vita on us in the next year, they will blow past their 7th gen counterparts easily. But, if they all sit back and only focus on games, and only try to dabble in multimedia, then the likes of Ouya, Amazon Fire, Google, and Samsung will steal a massive amount of the market with android based consoles.

Sony shipped 14.2 million consoles in 2006 so even accounting for those numbers the total console sales are still ahead for the start of this gen (2013 numbers).

This all looks pretty typical of another console generation and typical product life cycles.

If that's so, yeah, slightly ahead. Now add Game Cube numbers and things must be even.

And now take into account how frontloaded PS4 and XOne were (1 month in 2013 will most probably account for more than 6 months in 2014) in comparison to PS3 and Wii (1 month in 2006 accounted for much less than 6 months in 2007). In my graphic, 2013 got benefited by that. The truth will come out when we get the totals of 2014 and 2015.

Otherwise, going by your logic, we must expect a massive growth of total sales this year (as we saw from 2006 to 2007).