Firstly, it's taking place at the Excel Centre. Which...I've nothing against the Excel centre personally, but I gather that Excel's hired-in security caused problems at Worldcon, which makes me a bit dubious. Also, just the size of the venue leads me to suspect that they're hoping for a large scale event rather than a properly intimate convention. Maybe I'm biased in that regard.
Secondly, they announced it on February 5th. It's taking place on April 24th - 26th. That's about a two-and-a-half month lead time. I mean, presumably they've been working on it behind the scenes, but short lead time = less publicity than desirable = less attendees than desirable, I'd've thought. The Doctor Who convention in November 2013 was announced around June of that year, a good five months ahead (may have been longer). Only today I had an email announcement about a Lego convention at the Excel centre that's taking place in December
Thirdly, and this is the thing that's really going to bite them in the bum, there are five tiers of tickets. The cheapest ("standard") full weekend ticket is £44:00, Silver is £125, Gold is £295, Platinum is £595 and VIP is £2995. The real kicker? You can't get an in-person Benedict Cumberbatch autograph unless you've got either a Platinum or a VIP. And if you get either a standard or silver ticket, apparently "autographs, photoshoots and talks may be available to purchase on the day for a set fee in addition to this ticket." May be available. Essentially, you have to get a gold ticket before you get guaranteed access to any of the things that are normally a given at conventions (like stage talks and autograph sessions; and even that's not guaranteed at gold level, which offers "Priority entry to autograph queues by ticket number after VIP and Platinum ticket holders". High ticket number? Too many VIP/Platinum ticket holders? Tough luck...).
This cannot possibly end well.
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