The 12.5% corporate tax rate is still one of the lowest in the EU, why would the jobs go elsewhere ?
So whilst the Irish tax rate may be the lowest, the cost of operating a business there may, in total, be higher than somewhere with a higher tax rate.
Obviously I am not suggesting they will go elsewhere (given they cost of moving is probably very high) but something worth considering.
How would other firms be confident their taxes wont retroactively change? The Irish government is in no position to provide guarantees.
Also, it wouldn't make sense. A normalisation maybe, but harmonisation is stupid and a sure way of creating poverty, turmoil and destroying the EU market by removing jobs hence consumers.