New Season and Champion Mastery?

(Preemptive apology if this is on the wrong board!)

I was just wondering how champion mastery is impacted by the move to Season 7, and none of the announcements I've been able to find over the past month or so seem to have mentioned it. I know that earning chests is a one-per-champ-per season thing, so I'm assuming we can earn a new chest for all champions when Season 7 begins.

I'm more interested in what happens with rank/mastery level, especially since earning level 6 and 7 required investment of essence. Will those levels persist across seasons?