So, on a Lyn choice playthrough, Lilina has Power of Gold from Farina. Don't worry about what this is until it's finally codified, but the short version of the story is that it's easy enough to hit if you never buy anything in the system we had planned that I feel uncomfortable leaving the Arena situation the way it was. Especially given the Unbreakable weapons change.
So the Arena changes. keep in mind that Arena's have already been changed to have limited fights.
Fights no longer pay out, and the cost to buy in is reduced. It's still paying for EXP. Think of this like the Drill Grounds in FE12. You are paying for a fight so you can get EXP and level up dudes who've fallen behind.
After clearing out an Arena, then you'll be rewarded a cash prize, which will likely be balanced around what you had to pay to fight. OR you will receive an item that would have cost more to buy, like spending 250 on 4 fights, and getting a Steel Sword. (Steel Swords are 2000 G now for those who haven't watched the stream)
3.On-Map Arena's are single-shot boss fights, like Ch.7 has you fight Fir, who if you beat her say... gives you an Elixer. This lets me re-purpose the on-map Arena's in a way that doesn't require me to disable them or have them double up with Arena's in the base.
This lets me control the flow of money into the hands of the player, stopping Power of Gold from getting out of hand, and also answering the question of "Well weapons don't break, what do I do with my Gold?" This isn't the only answer. For example, occasionally when you speak to Merlinus or another shop keeper in the base they'll, before launching the store say "Hey, we found someone offering a weapon not available yet for an inflated price. Would you like to buy this for a quick boost in equipment now for some liquid funds."
This is mostly early game focused, because by the end-game you have the 15k S-Rank merchant and the Secret Shop to spend money on.