Ah sales predictions. They can be so hard to get right. Not only do you have to predict sales of consoles but you have to take account of the company’s behavior. You can have everything right but your prediction will be wrong if you don't take account what a company will do. Anyway for the many years I have been on this site (5 years :P) I have yet made a prediction. Shame really. This is where it ends. 

MY PREDICTION: 8th Generation  HOME  console sales will be closer to 5th generation total than 6th generation.  Meaning total sales will be closer to 5th generation's 140 million than 6th generation's 200 million

Justification for my prediction: The Home console  market will easily miss 6th generation totals. How do I know? Well for starters the PS4 and Xbox One will have to sell about 80 million each to reach the 160 million sold PS2's. The PS3 and Xbox 360 was only BARELY able to make that  with about a total of a little over 160 million (164? right now I think) for the HD twins.  The gen 6 number does not include GC or Xbox numbers. That would bring the total to 200 million.  Granted the PS2 sold for a long time after the intial generation ended. The HD twins will probably end up with about 175 million together. Here is why this is important

The PS4 will have no doubt on passing 60 million. However Xbox one is not gurreteened that number and especially not Wii U (No offense Nintendo but you still make good games and is my favorite console maker). Combined they will not outsell the PS2 numbers. The systems will not have a long generation like last time or peak so late. (The HD twins peaked at about 5 to 6 years old. This is unheard  prior to any past console. Including PS2) 

According to my predictions The generation would have 

PS4: 65 million Xbone:30 million Wii U: 15 million. Total:  110 million
Honestly those totals are horrible so let's be more optimistic 
PS4: 80 million Xbone: 40 million Wii U:25 million Total:150 million

Again this seems the most optimistic prediction I can put up.  Since every generation lasts about 5 to 6 years. I expect the PS4 to do about 10 mil a year. About 8-12 million a year. For Xbone I see about 5-8 million a year. Wii U will be between 3-6 million a year.  Of course this by predicting the current trend and taking note of future years.

How to tell if I am right or wrong on this prediction: 6th Generation sales are 200 million. 5th generation is about 140 million. The mid point is 170 million units. In order for me to be right, sales have to be UNDER 170 million. 

The so called counter arguments (Sorry this is mandatory)

"But the Super HD Twins are selling faster than the HD twins!"  So? The 3DS was beating the DS on their first year. Wii was trending above PS2. Yet we all know nether will out sell the DS or PS2. 

"This generation will last longer!" No, MS and Nintendo will probably try to get the jump on Sony next time and launch a little early. (5 years?) They probably both know they won't win this generation and will try to get an early lead for the next one.

Closing statements- Yes I believe the PSP's lifetime sales will outsell them all mwhahaha! Also if you disagree with me POST your lifetime sales and reason stating why!

I think somewhere in between the 2 is likely. Without the Wii's numbers this gen it's definitely looking to be like 5th or 6th gen.

ps4 with all the hype is doing only 100k per week, while ps3 last year used to sell 120k and sold 8 mil...
XBO and wii U doing worst.
It is early to predict, but seems that this will be a bad selling gen.
In the end, will depend on how long this gen will keep alive.
if it is a long gen, id compare to 6th gen, if its a short gen, 5th.

There's a major factor people seem to be forgetting that goes with Sonys long console legs - Price cuts. I think the PS4 will be hitting its full stride after reaching $300 per console and that may very well be within the next two years. Sales will be slow to start but this is a marathon, not a race.

In regards to X1 however, I'm honestly not going to try and predict how they'll do. Their story is interesting to observe for sure, and I think our situation for the entire industry is unprecedented. Making predictions off the past does NOT point to the future.

Ps4 doesn't have that many games yet. Once fall gets here I think their sales are going to explode

Nah, a new generation has never sold less than the previous, so I think the trend will continue.

PS4 isn't even doing good anymore, it's simply doing better than the competition (barring 3DS). 3DS and PS4 are average, okay. Maybe even a bit under.

What makes them look good is everything else that's doing even worse.

Probably. 150m - 160m is a safe bet.

Hmmm, I personally see PS4 doing 110-120 million (10 year lifecycle and all), XBO could manage 60-70 million, and Wii U 20-25 million.

It is really hard to tell. Like you said, without knowing what a company is going to do, or what missteps will take place, predicting a full gen is nearly impossible.

I think that there are to many factors in place to make a solid prediction. Sony has IPTV, Project Morpheus, and potential to have market share to gain easy 3rd party exclusives. Microsoft has the One OS future with Windows 9, and The Cloud. I think only Nintendo has nothing that can change their fate.

Then there is the possibility of new sales models. If Sony's IPTV takes off, and Microsoft expands their offerings on XBL then they could potentialy sell on a subsrciption model like MS tried late last gen. There is also the possability that we seePS4 and XBO 4K models in a year or two when the first die shrink is mature enough. If the later happens it could be a complete shift in the console buisness as we know it.

With all that said, I will still predict that this gen will sell better than than gen 5 or gen 6. Something in these consoles will spark sales and propel them to major success. It may be one of the above, or it may be something completly different. PS4 and XBO both have the potential to do much more, and with Sony and Microsoft constantly in a battle to one up each other they will be tap for every ounce of their worth.