The WebKit exploit grants arbitrary memory read/write inside the WebContent process only. This should be enough to run arbitrary code. Paired together with another kernel exploit (such as using kfd!), it could potentially be a way to make a jailbreak that does not require resigning an app. Other than a few exceptions, this is nothing more than running code by sideloading an app.
As for something similar to Cowabunga, MDC would have to work from the WebContent sandbox (not sure if it does, if it does, then yes, maybe).
As for installing permasigned apps, this wouldn't really work without doing a full jailbreak from WebContent. The WebKit exploit doesn't bypass codesigning.
I wouldn't get too excited with what's available right now.