Just a little confirmation on timelines. Currently the Gold Chest says it will update in 27 days. This lines up with March 24th, the projected release date of Suncrest.
Going by the above spoilers, to trait the 7 troops released with Suncrest (remember, an epic is released the following Monday) you'll need:
1 Yellow/Yellow (scheduled for Apr 10th)
2 Green/Yellow (scheduled for Mar 20th)
14 Green/Purple (scheduled for Feb 27th, Next Week!!)
3 Yellow/Purple (Not scheduled)
3 Blue/Red (Not scheduled)
16 Red/Yellow (Not scheduled)
So if you're wondering what kingdoms to target for Explore farming, there you go. And you might want to buy some extra next week so you've got excess stones for the Green/Purple Rare and Epic.
*Disclaimer, all information subject to change! Both kingdom troop colors and event week colors could shift.
edit: changed totals b/c I keep thinking rares are 3 and ultras are 4