I guess not, fantasy settings are more popular on RPGs, even a very popular non-fantasy RPG series like Fallout needed three titles on many platforms to sell more than 30M.

It might go on streaming services, how do you track that? Unless they're all like google stadia and you still have to buy the game.

Standard high fantasy is way more popular than anything sci-fi. Can it sell more than Fallout 4, probably not.
Fallout 4 sold some 15 million units. Deus Ex games don't even pass the 5 million. Mass Effect games are under 5 million, yet for some reason people expect this to beat 30 million? Witcher 3 sold some 20 million copies. So I'm guessing 10 million as sci-fi is half or less as popular as fantasy.

Streaming services will grarantee it will be playable in any device with a screen and internet connection capabilites.

Well their are many Keanu reeves fans so if they all buy one it will sell a few billion.

You guys seem to not realise that CDP is creating this game and expecting it to be MUCH more successfull than Witcher 3.
Wild Hunt sold almost 10 mln copies first year and 20+ mln up to date. It was done with only 40 mln consoles base in 2015, when game launched.
Right now they are using RDR 2 as benchmark: 23 mln units in the first quarter.
When C2077 arrives, the console base will be around 160 mln and it has huge advantage over RDR, with its PC launch. You should probably knew that Steam users count is much bigger than i 2015 as well.
Preorders for Cyberpunk have already started and the numbers are significantly bigger that W3 ones. You should be expecting a couple millions of preorders right before next year's premiere.

Bethesda will probably continue to re-release Skyrim on everything so catching it will be hard

My money is on no, it won't outsell Skyrim. It looks amazing, and I hope it sells in the 10s of millions, but I doubt it will even outsell Witcher 3. It'll be a while before the Skyrim total is broken by another RPG. I doubt even Elder Scrolls 6 will manage it now that Bethesda's reputation is damaged.

You doubt it will outsell Witcher 3 ? The chances of this happening are minimal.

C2077 is much more anticipated than W3 back then. Console base is 3.5 times bigger. Steam user base is significantly bigger. GOG as well.

Preorders are much better than W3's. CDP Red fan base has also grown. Company will throw more money to promote game in US.

W3 sold 4 million copies in 2 weeks - I predict that Cyberpunk will beat just before launch date.  

PS4- Userbase (100m)- 7-10m
Xbox- Userbase (45-50m)- 5-7m
PC- 7-15m
Next Gen Console- 5-10m

Honestly I could see Cyberpunk 2077 selling more than Skyrim. CD Projekt Red will probably employ the GTA 5 strategy which involves releasing a heavily anticipated game right before the launch of next gen consoles so during the peak of current gen with maximum userbase then relaunch for next gen with a major feature perhaps? GTA 5 (First Person View)=Cyberpunk 2077 (Third Person View)?

But of course GTA is the biggest and most notorious game franchise in existence with 5 ending up selling 100m (wow)
However a lot of hype is riding onto Cyberpunk especially with Keanu Reeves so I believe 25-30 is very possible

The real question is: will Cyberpunk 2077 be the most successfull entertainment launch ever ?