This is a bit premature, but I thought I post it before I forget.
After all Season 2 stages have been released (which should be end of march 2019), there’s no way to get coins aside from chests. The 2019 seak peek hasn’t mentioned if SG has plans for this, so i’m going to post my own idea.
“Collect coins” quests (I & II) similar to the “collect gems” quests. Even though i’m not a big fan of the new mechanics, the quest could have a stage effect like “poison mist” or “underwater” to make it more interesting.
Storywise it could go “raid ruins in the jungle/swamp” (-> poison mist) and “search an underwater cave for secret treasure” (->underwater)