I don't think there ever was a loophole and I don't think the loophole has been closed as such. I think that (some) people were resolutely ignoring Revenue guidelines as quite clearly set out in their Revenue Stamp Duty ( what is a First Time Buyer) leaflet but that when Revenue made it clear that they were likely to and actually were checking out purchasers who had claimed FTB stamp duty relief and had clawed back Stamp Duty not paid, plus penalties and interest, that the tide began to turn.
There will always be people who try to evade tax. There is, however, an almost certain inevitability about being caught out.
mf