The numbers going to/via Dubai have been pretty stable for years at around 230,000 pax a year
In 2007 the airport had around 5.7 mm pax - cp 4.8 mm last year - so you could argue that there is easily another 900,000 pax out there - but a new long haul airliner would have to take over 25% of that extra demand to make it work I guess - that's a big ask