You worry about everything. You're such a grown-up.
I did recognise Matt as soon as I saw him (from having watched Ruby in the Smoke), but I was very surprised.
He was chosen for his acting skills and the way that he looks both young and old, not because he's a younger face for the "kiddies."
Who says they need to bring back an iconic villain for series five? That's what RTD chose to do every year, but 2010 Who will be a completely new production team, and they might not want to do that.