Early results with Asik/Howard starting at PF/C were good, especially the last two pre-season games. The offense wasn't optimal, but the defense was suffocating. McHale has mentioned playing different starting PF's based on matchups, so I imagine he might not start all 82 games that way. Also I feel like just because they start that way doesn't mean they will play the majority of the game that way. I'm sure they'll stagger their minutes as the game goes on, especially as one or the other gets in foul trouble.
Lin has always made more sense as the 6th man, but I'm guessing Beverley has made himself someone that was good enough to displace Lin in the starting lineup as the better running mate for Harden.