I think it's a complete waste of time if they would make an artist work on a new loading screen just to add some roaring angry thing.
seriously, you look at it for 10 seconds and is completely unimportant to the game.
Agreed, Wrath login sucked, as did the music. TBC login was mysterious and really cool. The music was very fitting too.
WotLK's login music was almost quantifiably better than TBC's music... I never really got why people complained about sindragosa. She wasn't loud if you didnt already have your speakers cranked to unbearable levels.
As for the current login screen, I think it'd better if they added a few moving background details, like Alani flying around in the background, or something similar.
“Do not lose time on daily trivialities. Do not dwell on petty detail. For all of these things melt away and drift apart within the obscure traffic of time. Live well and live broadly. You are alive and living now. Now is the envy of all of the dead.” ~ Emily III, World of Tomorrow