Arena: Cards Picker
Arena Picker is not supported anymore
As far as the arena tool, we just didn't have the resources to continue working on it with other projects going on and constant updates each month. I wouldn't say it will never come back but until Arena captures a larger share of the player base it will be hard to justify putting so much work into maintaining something like this with hundreds of cards in the pool.
In the meantime, you can check out guides from Gravekper on Arena.