Having passed through Dubai 20+ times since October 2008 and after hearing many (varied) stories from others about Dubai, I assure you that there is not a hope in hell's chance that DXB as it stands could support another major carrier based there with 50-100 aircraft (as I suggest).
During peak periods at DXB there is a shortage of slots... Yes if you fly in in the afternoon there's plenty of space but between 8pm and 8am the airport is essentially at capacity.
Yes DWC has been built but currently it has a single runway with one small terminal capable of handling (correct me if I'm wrong) 7 million passengers per year? Comparable to Newcastle, Bristol or Edinburgh. Emirates won't be getting a whiff of Dubai World Central (Al Maktoum) until after 2025 when it is intended they move there. Currently the plan is Flydubai move there within the next 12/18 months and then either swap back in 2025 so EK flies from DWC and FZ from DXB, or all airlines move to DWC. It's all a bit up in the air at the minute but if Emirates wants to avoid stagnating for the next 10 years they need more room at DXB and that is being done by building the new terminal (T4/Concourse D) for foreign carriers - which will be opening very soon - and giving all of Terminal 1 and 3 (concourses A, B, C) to Emirates then moving Flydubai out to facilitate expansion. What will then happen to Terminal 2/Concourse F, I do not know, but I believe that these are the plans.
I foresee a squeeze at current DWC when 48 737 800's pitch up outside...