All countries have visa issues, and visa is a major consideration when choosing a location for wikimania (or at least was a major consideration this year when Hong Kong was chosen). It was also a major consideration, and was taken into account when DC was chosen. There is only so much a local team can do about this, and usually the best solution is for the local team to have close contacts with the relevant consular officer, and for the attendees to apply for visa as early as possible. The only true solution is diversifying location for holding the conference and this was indeed done the past years.
I do not think a permanent WF Wikimania team is a feasible or a successful option. An advise may be given, and is welcome, but it is for the local bidding team to do the work.
I plan to lead a discussion during the Unconference about bidding for Wikimania, and preparing for one, and invite you all to attend.
Deror