Winged Pikmin already removed one of the primary functions of Blues (carrying things through water and reaching things over water) and reduced them to "Oh yeah there's a fruit in the water and only blues can get it".

I think the only other instance they're required is building a structure to get captains and other Pikmin across. One time. Maybe they only used it once in Pikmin 3 but hey maybe they can add more things like that to Pikmin 4.

Except here comes Ice Pikmin to take that too. Why bother having Blue Pikmin? Just to go "Oh yeah better grab the one thing in the water" and not use them otherwise?

Other than something sitting in the water needing to be grabbed they will serve no function unless they add something like that water enemy from Pikmin 1 that could only be killed with Blues because its body was made of water.