If the government start taxing individual expat then it will open a pandora box. People will then demand parity with local nationals regarding subsidized housing, real free medical care, child care support, schooling etc and maybe many things more as time passes.
Though i think that is all small talk, Dubai gov has been dwelling on this for a long but has not dared to go ahead on this issue.
Most probably it will be done indirectly t by increasing the visa fees.....that all it will be...chao