It is suggested to host IRC on wikimedia servers. The argument being that Freenode may vanish.
There are several good reasons against it. *It does cost extra bandwith. *It means that the Mediawiki server park becomes even more complicated. *This means that there are more eggs in the mediawiki basket. *All this work is done to a large extend by volunteers. The current infrastructure needs all the attention it can get. IRC on wikimedia servers will devide the attention and that is not a good idea at this moment in time. *There is no reason to believe that Freenode will be gone in the near future.
It is more important to stabilize the current servers and make them more reliable.