Pacquiao is much like Cazalaghe and even our Daniel Geale: quantity over quality of punches. All three are incredibly fast and 'constant' in their punches, but they lack 'power' and 'strength' behind their punches.
Cazalaghe showed it easily. The hard thing about fighting against the constant 'flurries' from such guys is that you fall behind on POINTS really fast and early in the match. You have to win by KO against guys like this - but its hard to throw a punch against someone who is already throwing punches.
That's where Kostya knew how to take punches for the benefit of a better hit thrown (doesn't work against a heavier opponent with stronger hit from a higher weight division like Phillips).
Hatton just 'wore' him down with more youthful energy and more punches for a points win other than the 11th round 'resignation' by Kostya.
Mayweather is not a 'machine gun' of pellets like Pacquiao. He is ultra defensive and pure 'counter-puncher'. Kostya would forget about Mayweather's head (well hidden by that rolling shoulder) and just body punch which gives him a good position against Mayweather's 'counter attack'. Kostya would have the strength to make those body punches count. Not only that - Kostya showed with Zab Judah that he is not affected by guys who try to mentally intimidate the oppenents before the fight with trash talk and other games. Mayweather's 'Money' attitude falls short of Kostya's 'Professional Boxing' attitude.
Kostya would easily agree to fight Mayweather for 'nothing' and thats where Mayweather would have no 'bait' to hook Kostya with a 'sucker punch'.
Mosley was very fast (too fast for a coke induced Shannon Taylor thanks to Jeff Fenech) but he was too erratic in his styles and tactics. Still, the dude has never been knocked down. Kostya would knock him down in the 5th Round. Simple as that, let alone as simple as Mosley was.
De La Hoya? Heavy puncher and relentless forward moving boxer who overpowered his opponents. A test of strength for Kostya with someone who would go toe-to-toe like Pacquiao but stronger/slower. Kostya was versatile enough to know when to go forward and when to go back. When to be a Boxer, when to be a Fighter (Mundine could only Box, never 'fight'). He also had just as much 'persona' as the Golden Boy did and as you can see, both have gone on 'after' Boxing. La Hoya a Promoter and Kostya a Trainer (Coach).
So there you have it. If I have it worked out with those four, then I'm sure Kostya had em worked out a long time ago.

I would not be in the least surprised to see Kostya return to OZ one day to train a 'Champion' or bring one from Russia with him. Either way - "he'll be back."