An odd request lets say the flight was full that would be 42 passengers. I wonder just how many of those 42 would be users of this forum and then of them how many would have been attracted by the subject header to click open and then of them how many of those would have had or noticed if a roller bag was allowed. of course there is no guarantee that a week later the rules may be interpreted in the same way if discretion was exercised or was not exercised
There are clear guidelines as to the size of bags allowed as cabin baggage and what you can take as hold luggage so please assume Emirates will charge you for any luggage in excess of the rules and if they do not then count yourself lucky