PS4 - 4.5 million copies

Xbox One - 3.5 million copies

PC - 2 million copies

-The gameplay looks awesome

-Supposedly will have great DLC

-Will be bundled with Xbox One for a while

-Great graphics and art style

-cool enemies

-Highly aticipated all around

The only thing holding this game back is the lack of online modes (does it have any??)

I doubt it. Maybe 8m.

I don't think it'll sell nearly that much. It would be awesome if it did, but I don't see it. Dragon Age Inquisition is a similar game and VGC has it at approx. 3.3 million with all platforms combined. There's also the fact The Witcher is a PC franchise so I expect it to have the majority of sales.

Wait 2 million PC? You do know this is Witcher right. 

...no. 3,000,000 / 4,5000,000 is way more reasonable.

PC: 2,000,000 (500,000 retail)

PS4: 1,500,000

XBO: 1,000,000

But if will happen, will be deserved. That for sure.

PC numbers are far too low.

The Witcher 1 sold 1,7 million copies on Steam alone http://steamspy.com/app/20900
The Witcher 2 sold 2.7 million copies on Steam alone http://steamspy.com/app/20920

Mind you, the Witcher is a GOG original franchise, meaning it sold a ton on GOG as well.

The Witcher 3 will probably sell 4 million on PC, maybe even more.

Namely if Witcher 3 becomes modable. 

I think you overestimate impact of modding on sales. 

PC sales will be higher, console sales likely lower, in my opinion. The Witcher was never a big franchise outside of PC, and even though I think it will grow a fair bit due to being open world; I think 4.5 million for PS4 and 3.5 for One is way too optimistic.

That said; I hope it sells that much since I adore the series, GOG and CDProjekt in general.

From less than 2 million to 10 million is a giant jump so I am on the nope train (even though I wish it did T_T)