There will be an Alternative Advancement system, think Everquest. These will cost exp. AA's can be expanded and expanded to continue to give exp coins value after all are capped. But the mining process will take years, and with spells, weapons, which both can have alternative variations "trees" - and people will likely want to play around with diff setups. Unstacking exp coins come with a fee, which will keep demand there.

The goal is to allow the feeling of accomplishment IE, I powered up my deck, and it stays powered up without losing value for exp coins.