Very unlikely. Even if we could support it from the server's end. We already have extreme measures in place such as limited sight radius in places like Dalaran to an extent of like 20 meters or so. We could apply more extreme measures to the server to allow more to be online. Even if we didn't have to apply extreme measures like this at all, allowing the population to increase further still would not be ideal. This version of the game was not designed to support 12,000 people being online as it is. The game becomes very cluttered, especially with high EXP rates and everyone getting funneled into focal areas like Dalaran, or only a few zones that are limited to one continent. The game already starts to break down at 12,000 players in certain aspects, such as material farming, grouping outside of instances, etc. Nevermind allowing it to increase further.
What would be more ideal is that some of these players consider playing on Lordaeron instead, or potentially on any new realms that we may choose to release at any point in the future.