This was already possible on desktop using the following flash polyfill: https://github.com/zeroclipboard/zeroclipboard. So on desktop at least this doesn't introduce any new threats, so this seems a little strongly worded to me.
Except that this is baked into the browser and affects mobile. It's also been discovered that your clipboard can be hijacked by purely loading a page. So yeah, I think the threat is very real and very obnoxious.