@Gregory, it's too early yet for us to speak about CDF Player, as that is some weeks away from being released. We can certainly mention some new features of the plugin as now available with Mathematica 10, mainly contextual scaling and being able to pass parameters into the embedded content via the DOM.
Here's a community thread discussing scaling, and some potential confusion associated with it:
http://community.wolfram.com/groups/-/m/t/236023
As to the handling of parameters, we'll be following up with more details, but as a teaser, I'm attaching an HTML and CDF file demonstrating a basic example of how it works. Bear in mind that this is a non-dynamic method -- the page and plugin content must be updated/refreshed for any parameter change to take effect.
Attachments: