“Cross country” routes over EWR is definitely out of scope, as per the TWA inspector‘s report where it quotes DfT‘s intentions.This was discussed earlier on in the EWR, for a moment it was 'up-scoped' for long distance paths, and then de-scoped so this might have fallen by the wayside. I agree it makes a lot of sense - opens up a lot of new journey pairs, and overall, it's a heroic 'not-London' output of EWR. Would be possible a lot sooner than Cambridge!
The MML quadding up to Kettering would help this too, but the 'Bedford station future/state mystery' hangs over it. Lord knows where they thought a HS2 to Leeds would turn either.