Parser 2011/The big picture

MediaWiki as we know it had its basic architecture set in 2001-2002, based on the then-needs of Wikipedia migrating off of UseModWiki. This has locked in a number of assumptions which have been difficult to break out of.

What's changed?

We've also seen some interesting changes within our own community which can point us at some interesting directions:
 * Custom user and site JavaScript and styles and l10n messages have made a lot of customization and some local features possible that would never have gotten done by core developers. With the in-browser JavaScript+HTML+CSS environment only getting awesomer as browsers evolve, this is a key environment for feature expansion and creative content creation. Make it easier to create and share things; find ways to remove bottlenecks to sharing code between users and between sites, and making it safer to do so by devising restricted execution environments.

Values
Major future-oriented projects should consider the core values of a wiki environment. What are some key properties of wiki, and what are current holes in that that we can fill in by modernizing?