The main problem with this is unlimited liabilities - if you are a member of the association and the association has a dispute with, say a venue, they could sue any member of the association as they would be jointly and severally liable.
Yes, and quickly set aside. When v1 was setting up we envisaged some substantial donations being made to WMUK and I don't see that being any less likely this time around. As a general rule, companies don't like giving money to unincorporated individuals as there is a whole lot of risk; they want a 'body corporate' which has to be public about everything where an unincorporated association can keep just about everything private.
Yes, we've also considered it and quickly set it aside, for much the same reasons and others. The fact that the board could be held liable for pretty much everything is an issue, as is the fact that any contract with the association would actually be a contract with the members of the board personally - would the WMF even want to sign the trademark agreement with individual Wikimedians (I'm not sure what happens with contracts like that if there's a change of board, but it can't be as simple as with an incorporated charity where there is no issue whatsoever)? Also, if we're as successful as we hope to be in the long term, there's a possibility of hiring staff which works much better if we're incorporated (if it's even possible otherwise). An unincorporated charity cannot own land, although I doubt that will be an issue (if we want an office, we'll most likely rent one).
Basically, associations work best for small charities that never expect to grow and have an extremely limited said of aims (the local school's parents-teachers association, say). That's not us.
BTW, Alison, since you've been talking to Companies House, I take it things are moving forward with the winding up. Do you have a timetable for that? While it's not essential, it would be great if the old chapter was completely gone by the time we get to the stage of wanting to sign an agreement with WMF (a couple of months yet at least, I would expect).