Decks to Beat
I am currently testing this card on MTGO, and it's been fantastic so far! I'm not sure if I should call my deck Storm with Belcher, or Belcher with Storm, but it's both.
It's essentially a storm shell, with no Bargain, and 3-4 Bolas's Citadel. I'm currently using Land Grant, a singleton Bayou, and Tolarian Academy.
I can't post a list because it's been changing multiple times each day, but I will say that the deck (and Bolas's Citadel) have far exceeded my expectations, in every aspect.
I believe the test on MTGO was just to gather overall player response and maybe any meta major shift. Since most people seem to enjoy the mulligan gameplay-wise and nothing huge happened in any format, I think there's no reason not to adopt London Mull - at least from the MTGO test perspective, let's wait for Mythic London this weekend.
I think that if the game experience is improved, there's no reason not to implement it. The worst case scenarios are changes on B&R lists or even pullback/change the Mull 1 year from now, which are fine by me.
I've spoken with the Sisters of the Flame, who are currently working on a location for a Sunday Old School event. I may have that sorted out for them, but need to speak to Andrew and Paul.