It is very simple to control the epic market.
The titan market will now get 'recycled' due to tiered epics, sure.
But this doesn't change anything for RP epics, which are totally overpriced compared to titan epics, atleast over time.
The simple solution would be: Have some epics reserved for RP, some for titans.
Meaning, the gloves/helm/ammy for example are invented from RP.
The rest of the epics you get from titans.
Presto, solved.
Plus you 'fix' activity in GvG with this.