The only thing the prefix system threatens is a few unimportant browsers that arguably shouldn't even be around anymore and the pride of the w3c.
And you want to save them, by throwing the future of the web under a bus?
For example: webkit devs think of a new property. They build it, they like it, they make it publicly available. Chrome guys enable using this in the dev and beta channel. In a couple weeks they have feedback on performance and stuff. Whatwg convenes, they finalize the details, webkit guys make a few adjustments (and it's fine because there's only 2 webpages on the entire internet that's been using it for a month tops) and then soon it hits the stable channel. This is what we need. Fast updating browsers could rape the benefits of such a system very nicely, fast updating is what we need to let the web evolve fast enough anyway. Slow updating browsers can go die in a fire, they are just as slow with supporting everything else.
Also, not to nitpick, but opera on the mobile front isn't unimportant. It's the only alternative to webkit, it's nearly ubiquitous and not a bad experience on mobile.