Nice. I made this sugestión a while back, but it would be 1 emote that would interact differently depending on which subclass you have equipped.
Hunters:
Golden gun: revolver twirl like revolver ocelot from metal gear
Blade barrage: juggle knives
Arcstaff: a more artistic twirling of the staff, like in the new subclass tree has, but all around the body, switching hands, basically put on a show
Voidbow: basically trickshots with it, shooting at smokebombs.
Spectral blades: butterfly knives tricks
Titan:
Striker: shadowbox with arc energy surrounding the player, 2 titans could put on a boxing match if timed correctly
Thundercrash( no idea yet, feel free to suggest)
Sentinel: (no idea, if you know something artistic or badass to do with a shield please share)
Burning maul: summon the mail and mount it on the shoulder, like someone would while waiting with a Warhammer
Sunbreaker: (no ideas yet), maybe juggle 3 flamming hammers
Warlocks:
Stormcaller: make an electricity arc with it's hands, basically slowly open it's hands and end up in a powerup posture with electricity jumping from one hand to the other forming an electrical arc
Chaos reach: basically the same as stormcaller, but concentrating the electricity in a ball in front of the player.
Nova bomb: basically meditate floating above a mini slova bomb.
Dawnblade: start flailing the sword and after 4 or 5 swings, sink it into the ground and kneel there, like a knight would
That is all I came up with, any other ideas are welcome,