Well it says this:
So, just like it was in the off-Season during patch 7.0, then you won’t be able to earn Duelist, Challenger, Gladiator, or R1. Those rewards will be locked-in based on people’s ratings on the last day of the Season (when the patch is released).
You will also not be able to earn the Seasonal Elite PvP Armor Set or the Seasonal Mount (the tiger), as those will retire on the last day of the Season as well.
You will however still be able to earn the regular Arena rewards, like gear from winning games and normal Arena achievements like Three’s Company: 2700, or similar.