WebKit is LGPL and BSD licensed though. I don't care about a monoculture if it's a culture where everyone gets to modify the innards for the greater good.
The problem isn't making changes to the source. The monoculture or de-facto standards come up because those are the rendering engines used by users. You can make WebKit or Trident a billion times better but it won't matter to web developers or users until users adopt the new code.