On Sunday the 9th of December there is a "takover" by Magic Rock Brewery at the King William IV in Leyton. I have seen the list and there are four cask ales (the regular Rapture, Curious. Highwire and Dark Arts) plus 12 Keg offerings (I'm assuming that these are Keykeg not fizzy rubbish).
The keykeg ones would seem to be a mix of a few of their regular beers plus special "barrel aged" versions of others. I suspect that some of these may be a bit on the strong side.
I have yet to establish what the prices will be but when I have tried Dark Arts and Highwire as cask guests they were the same good value price as the Brodie's casks. I found the Dark Arts and Highwire to be very enjoyable drinks.
Given that there are only four casks, I can safely assume that there will be a good range of Brodie's casks on as well given that they have more handpumps available than any other pub I have ever been to.
I will add to this post as and when I get any more information.