Employer since 2001 permitted eligible employees to commence deferrals immediately upon hire instead of making such employees wait until the plan's dual entry dates. The employer can't use self correction because this error goes back more than 2 years and presumably is
significant. What is likelihood under VCP that the IRS will let the employer correct with a retroactive amendment providing for immediate eligibility?

That would be the preferred method of correction under Rev Proc 2008-50, provided that the amendment itself is nondiscriminatory.