Should probably clarify that if you do decide to keep the original PPR for more than 12 months and then sell it, only a portion of the loss will be allowed for CGT purposes
eg
You own & live in the House for 3 years (36 mths)
You then move to a different PPR but keep the first house for a further 14 months
Because the last 12 mths of ownership are deemed PPR, Revenue will consider that 48 of the 50 mths of ownership are PPR so you will only be entitled to use 2/50ths of the actual loss to offset against any Capital Gains.
Without getting into a discussion about house prices etc, I can't see how holding on to a property for a further 12 months purely to offset a Capital Gain makes financial sense. You could potentially lose more than the CGT saving if the property decreases in value any further.