i can't predict how it'll be tuned, but i think perfect tuning for clearing heroic would be, if guilds that have 885+ won't struggle much until they face guldan. Also, 35 traits for heroic.
That said, each heroic boss should be killable in ilvl equivalent to its normal mode drops. So for example if a boss drops 880 on heroic, it should be killable with 865 (that's for organized groups only).