Ichor was introduced as the “silver/time sink” for the bajillionaires of this game. It doesn’t have to be just that though.
Combine ichor and the previous forms of improving gear and you have a pretty robust “upgrading system” for HG gear. To balance out the tiers, you can have increased success rates (substantially) for lower tied gear. Orange would have the lowest success rate, while blue would have the highest to ichor.
