its simple. nothing that wasnt in the 1.1 - 1.12 timeframe.
now there were alot of things that happened in that timeframe so wanting 1.12 patch with 1.5 av would still be within what was in vanilla.
or pre 1.11 shield slam changes for everything but naxx. that would involve adding in an aura to naxx which would be something outside of the 1.1-1.12 timeframe though so some people would not want that.
but yes . the core of no changes is nothing but 1.1-1.12 timeframe.
that would mean things like guild banks and transmog wouldnt be in.
neither would sharding or loot trading though either. or bnet.