Outward-migrating planetary system at Vega?

Well, it seems to provide a possible explanation for Vega's exozodi...

Raymond & Bonsor "Vega's hot dust from icy planetesimals scattered inward by an outward-migrating planetary system"
http://arxiv.org/abs/1403.6821

A system of planets between ~5 and ~60 AU would be able to explain the exozodi. The outer planets should have masses in the (mini-)Neptune domain 2.5 to 20 Earth masses. A Jupiter-mass planet beyond ~15 AU would be too efficient at scattering planetesimals for this mechanism to work.