Not just for bragging rights but to strike fear into the other team plus it would help to let your teammates know that they got a max nano teammate active and might adjust there tactics to add even more to the advantage. Obviously I play with randoms mostly, since this wouldn't matter if you mic'ed up and or in a squad, but for the rest of us it would be appropriate to have it announced.
I felt kind of dissapointed the first time I ever got the max nano at release, I was just waiting to hear "Alright!, one of our teammates maxed out his suit, show them no mercy!!!" But nada . Only "your maxed suit is good to go" sort of anticlimactic and your the only one who can hear it.