Finally, a dev response on this! Thank you for acknowledging us arena players.
It's crucial that participation alone will result in rewards or it will quicly die down again. On the other hand, with no win criteria they might end up in an AFK situation. It's a tricky balance.
Have the good rewards be for both rating and number of wins. You can eventually get a decent number of wins just by participating even if you aren't especially skilled so it would be a matter of perseverance rather than ability and luck for that.
As for what the rewards should be?
I would say, an exclusive colour crystal.
Maybe one for the top 10% of players by rating and one for players with over 50 wins, lets say.
Titles - again, have a few different ones for rating (like, 1500, 2000, 2500) and for participation (10 wins, 100 wins, 250 wins).
Exclusive speeder - but make it actually cool, like a tank or hovercraft or one of those big boat like speeders that everyone finds so obnoxious when you park them at the PVP terminal. Yeah, I want one of those.
Maybe an exclusive dye that is bind on pickup - the colour of champions.
I know theres only so much they can give us... but they still can give us tangible in game rewards, for both success and participation in arenas.