I could be totally wrong on what I’m about to say but if you always have a features weblog entry then if you do as you are wanting then you would never even get the chance to see one of the news weblog entries?
To that end (if I’m right in my thinking) then I’m a bit confused but if you don’t always have a features entry that satisfies that weblog search parameter then you might be able to do what you want in the following way :
Main Template
{exp:weblog:entries weblog="features" limit="1" search:news_featured="Yes"}
<h2>{title}</h2>
<p>{if no_results}<br />
{embed="your_template_group/news_weblog_entry"}<br />
{/if}</p>
<p>{/exp:weblog:entries}
your_template_group/news_weblog_entry
{exp:weblog:entries weblog="news" limit="1" search:news_featured="Yes"}
<h2>{title}</h2>
<p>{/exp:weblog:entries}
This way if there are no valid results for the first tag which just brings back the features weblog then the embedded template would run and thus bring back the news item instead.
Not entirely certain if that’s what you’re after though because I may have completely misunderstood by what I mentioned above.
Hope that does help a bit though.
Best wishes,
Mark