This is a very interesting question!

Like elphaba says, not everyone moves for money but there's no doubt that it's a BIG factor. I reckon the small amount of VAT that is proposed wont hurt the educated, higher earning expats too much but the imposition of an income tax would have a massive effect. BLM hits the nail on the head with her comments about the cost of living in Dubai.

The positon of the unskilled labour in Dubai is probably a more important one though. These guys have seen the value of their take-home pay plummet because of the dollar peg and they can't offset that loss by saying "ah well, at least the lifestyle is good". If the slave labour dries up who's gonna do the jobs that the the westerners/ emiratis won't?

Don't know if anyone read it but there was an excellent article in The Economist about the Gulf economies (and Dubai in particular) a couple of weeks ago. You should check it out on their website if you're interested.