Eventually guilds will hit a brick wall, it is inevitable, so they will probably add the 5% nerf however I don't think it will go up to 30%, maybe 10-15. They did it wayyyyyyy too early in DS and it had to go that high, this time around they are waiting to see progression start to slip off then I believe they will turn it on. WoD isn't for awhile so no reason to start nerfing everything yet.
Also they will probably nerf Flex too if they nerf normal mode since Flex is just normal with a 15% nerf anyways :P
I would rather they nerf the amount of trash by 30% if anything, takes way too long and all it is is AoE + AFK.