From what I've read, the only way to do this is to have the focus() event be triggered from a click event -- then the keyboard launches. Unfortunately the code I saw used an HTML button to focus and launch the keyboard -- which wasn't my goal of launching the keyboard without user intervention. Unfortunately, all my attempts at trying to "simulate" the click event failed to launch the keyboard, and for now, it seems that it is a known issue. Whether or not Apple will resolve this or not is questionable -- I can understand the reasons why the keyboard doesn't appear on just any focus() command, but it seems nuts that there's no obvious way to force the issue.
Now, a plugin might work, for this, but I'm not immediately certain on how that would work -- if the webview indicated it was capable of becoming the firstResponder and a plugin call told it to become firstResponder, that might do the trick? Alternatively, the webview might be using some other method to handling input, and that might not work at all... but it's a thought...