Although this topic was posted about a while ago. I thought I would bring it up again as the first company, Blizzard is now starting to comply with the new online gaming regulations from China. They are required to disclose “loot box item odds”. This might eventually apply to Gems of War if they wish to expand their market into China.
I would say that as a community we already have a fairly good idea what the Chest odds are (even without official disclosure) through our collective data gathering.
http://overwatch.metabomb.net/news/overwatch-blizzard-forced-to-reveal-loot-box-probabilities