Some mounts would be nice like the love rocket or a special pet for every event that would lead to a year around pet achievement (sort of like the What a Long, Strange Trip It's Been).
id like to see brewfest get changed now the dark irons allied with us( or some of them)
id also like to see some draenei and gnome style festivals, since they lack them.
I would like to see a new holiday event for music. Where we can visit a few concerts in different genres. How awesome would it be when we could go to Armin van Buuren in game. Build a big arena, fits perfectly in garrisons I think, where we can see artists and such. Maybe this holiday event can take place twice a year, or more, instead of just ones a year.
Most of the Holidays haven't been significantly updated in a while. They add new achieves and update armor rewards, but with account-wide achieves my drive to do Holiday stuff is non-existent. So I think the Holiday most in need of revamping is Children's Week. Maybe more stuff to do with your Orphan?
And A Summer Holiday in Late July or August would be nice. The "Mid" Summer Fire Festival starts at the very beginning of summer. After July 4th we have nothing really until Harvest Festival in late September.
I would like to see other holydays than the usual north-american ones that we see in the game today. Maybe some Latin American or Asiatic. There are really interesting options worldwide that can add some new good options to the game.
Making gear revards more relevant, and bigger chance for the Big Love Rocket, its the only one I miss from world events And maybe harvest festival could be a regular event, such the others, with achievements and other stuffs (pets, mount, etc.), not like today, a one quest nothing.
I would like a really new holiday event, because since nine years, we've got all the time to do all events again and again, have the violet protodrake multiple times.
Something with a very long questline during each day of the event, with exclusive bonus and achievement the last day of it. A dedicate faction just for this event.
Not f....ing tokens to farm again and again.
I'd like to see new achievements unique for each holiday, with a possible vanity reward for completing all of them (much like the purple proto-drake, but something fresh)