The description in the draft enhancements plan now has the re-doubling embedded in the overall 'electric spine' project. All I can glean is that it is more to do with overall line capacity than any explicit increase in Corby's passenger service:
Midland Main Line capacity (Bedford ^ Sharnbrook - Kettering ^ Corby)
This project seeks to deliver enhanced track capacity for additional services on the Midland
Main Line in the future. The scope of works for this scheme may include; doubling the track
from Kettering to Corby, new track and linespeed increases between Bedford and Kettering
and improvements in the Bedford area. The delivery timescale of these schemes will be
determined by the Midland Main Line electrification programme and the East Midlands
resignalling works.
Is one of the problems with the current setup that they have to leave some gaps in the otherwise regular service to allow for existing freight to run?
Paul