Hearthpwn

Set rotation mode/ladder should work like this in my opinion:

Ladder reset every month just like standard/wild that would come with a rotation reset.

Allowed cards would be one of these each month:

A. 6 random expansions + Legacy set

B. 6 random expansions + one of the core sets (we only have 1 now, but we will have another every year)

C. 7 random expansions + 1 random adventure set (like Naxx)

We should also have an autoban system that would work like this:

After 1 week the 40 most popular cards should be banned from the format. After week 2 we add 20 more cards to the banlist, and we do the same after week 3. So from week 4 until the next rotation (end of the month) we would have 80 banned cards.

Thats how I would do it, but most of the playerbase wouldnt like a format like this because it would require a huge collection and it would reward deckbuilding and meta-reading more than just brainless netdecking.