I also remember when they tried it on before, Angus.
As well as the time of the rumours about revaluing the Riyal; which turned out to be another "damp squib", thankfully.
But the dynamics are a bit different these days, I would suggest. Far fewer Western expats to worry about leaving, for starters. As well as the ever-increasing local population (to be "supported"), falling oil revenues, a different (younger) generation in charge ... and all the rest.
No doubt they are "testing the waters" again now (as there's a lot about it on the internet). My guess is that they will be trying to calibrate the amount - some expats might be able to shrug off 5% (say); but if it was as high as 20% then, yes, we would expect a mass exodus.
Meanwhile, here in the UK, I'll admit I'm far more concerned about (supporting) "Biomeds for Brexit"!