The infmaous gameplay spot currently has 4.6 million views. The live action trailer already has 3 million views.
Adding up all its major videos, infamous has about 21 million views. That's a lot!
Now comparing that number to Titanfall is pretty stupid. It's a different channel and different circumstances. Comparing to another PS4 exclusive seems like a much better apples to apples comparison. I'll use Killzone 6.
Killzone's most viewed video on the playstation channel has 3.3 million views, a lot less than infamous. In total, all Killzone videos only have about 5 million views. Infamous is DOMINATING. That's impressive, because Killzone has already sold over 2.1 million copies to consumers. If we break it up to views per video, it's still 1.25 million to 3 million. A direct correlation of views to sales would predict 3-5 million sales for Infamous's early life.
Do views correlate to sales though? Let's look at knack. Its top video has a million views. Total it has about 1 and a half million views or .5 million views per video. Going off VGCHARTZ the game has sold 0.9 million, or 0.6 million without the Japan bundle. Using Knack as the starting point, it shows 4-5.5 / 2.75-3.5 depending on if you include Japan or not. Those numbers are pretty close to what Killzone produces, so I'd take it as ok evidence that views do correlate pretty well with PS4 game sales.
TLDR: Youtube says Infamous will sell about 4 million before the holidays even begin.