I think Briggs is more than capable of making the switch. I offered this opinion about a month or more ago and Mike Detellier has since also suggested that Briggs could move inside. He likened the situation to Will Witherspoon who also moved inside and has done a great job for the Rams. Briggs has the awareness to be a very solid MLB. And his speed and ability to move sideline-to-sideline does not hurt.
As far as pure MLBs, a lesser known prospect, Dontarrious Thomas, could get a look at MLB. Of course, if we were to sign Thomas, I would still sign Briggs and put him at WLB to add more speed to the LB corps.