I agree it's certainly not a panacea for all the ills of the current system, but as the syntaxes converge it could provide a way for web devs to use one prefix without breaking the web or forcing minority browsers to adopt the prefixes of the majority browser.

And it is often the case that you're using an experimental style that's only available on one browser family which is then adopted at a later date by other browsers. This method would mean that as soon as other browsers adopted the style it would render without any changes or additions required on the web site.