Cash shop is why we left EQ2. If ever implemented in a serious way in Rift cash shops would be why we left rift.
Cash shops ruined EQ2, with devs no longer caring about creating content from the subs, but instead creating sparkly hats for cash shoppers and every patch finding 10 new sneaky ways to slip a little further down the cash shop route while each time claiming they weren't affecting gameplay much more than the last step, with each new step. I'd happily pay much higher Rift sub fees, especially if it gave more content faster.
SoE drove off their subs orientated playerbase by developing the "fremium" cash shops model, but never got the cash shopper/fremium type players to replace them and now they're in real trouble. Cash shops usually signal the beginning of the end for a MMO, and even if it generates a short term revenue bump it seems to destroy long term loyalty and viability just as much as it degrades the quality and integrity of the new content.