Seobaina: Yes, I mean that Emma. She was lovely, and I wouldn't mind having her for a DM if I end up changing districts.
Disneybex: I agree the layout of Westfield would work very well for this type of event, and perhaps even taking it out into the mall itself for a larger event.
However, I would have reservations about doing a London based one. I think while access to London is good (good trains/flights/etc), I think it's not central enough for everyone. It's not best placed to draw in/accommodate as many people as possible. Plus, parking is a nightmare
That was one of the beauties of MK - if you drew a circle of 1hr car travel time from that point, you would have encompassed a lot of the country. Try doing that from a London-based store and the result would be no where near as good!
I would definitely be in favour of a Northern event, to give those of you up there a chance to participate. As for London, maybe DS UK will have seen just how big pin trading can be and use the capital for a big pin event, similar to those that happen in WDW, like Pin Trading University several years ago, and Disney Pin Celebration - Trade City, USA, which takes place this year...