In 13w48b (not in 13w48a) resourcepacks are not abled to change the mojang logo. I looked at the files, they are in the same place as before.
Test it yourself: http://www.planetminecraft.com/texture_pack/16x-beta-17_01-coterie-craft-v16-regular-upd-6302011/
This should make a new logo. But it doesnt