As far as I know the casino coins to star gems hasn't been added yet as it was added in a later episode.
Challenge Mode doesn't have SG tickets either.
I am starting to feel that they intentionally did this so that people will spend money on SG instead.
Do have to add though. Even on the JP version the only way to earn SG from Challenge Mode is through the weekly rankings. (The Challenge Mode shop doesn't have SG Tickets.) And only the Top 50 earns 30 SG per quest. We don't know yet whether the NA version also rewards the Top 50 with SG tickets or not. We'll have to wait till Monday before we know for certain, when the rankings are updated/ends.
Don't get me wrong though. When it comes to earning SG in the NA version, it is disappointing to say the least.