One of the ways I propose replacing this up and coming feature is by just allowing us to call other selectors within a selector. I'll demonstrate:

<style type="text/css">
.bold {font-weight:bold;}
.blue {color:blue;}
.testingagain {selectors:.bold, .blue;}
</style>
<p class="testingagain">testing this out</p>

In the above code block the testingagain class would inherit the properties of both the bold and the blue selectors. Further more you could overwrite them, just as you do now.

<style type="text/css">
.bold {font-weight:bold;}
.blue {color:blue;}
.testingagain
{
selectors:.bold, .blue;
font-weight:normal;
}
</style>
<p class="testingagain">testing this out</p>

Hell, let's get jiggy with it:

<style type="text/css">
.cool {font-weight:bold;color:blue;}
.shout{background-color:red;text-align:center;text-decoration:underline;}
.testingagain
{
selectors:.cool, .shout;
font-weight:normal;
text-decoration:none;
background-color:yellow;
}
</style>
<p class="testingagain">testing this out</p>

Why I like this method

Because you can already do it now! You have to do it in the HTML like so

<style type="text/css">
.bold {font-weight:bold;}
.blue {color:blue;}
</style>
<p class="bold blue">testing this out</p>

With my proposed method it moves this into the css file for easier maintenance and readbility.

So what do you think?