We have been waiting for this!
The IRS has released IRS Notice 2015-13, which provides transition relief given the late retroactive renewal of the Work Opportunity Tax Credit program in December 2014.
Notice 2015-13 waves the 28-day deadline for submitting IRS Form 8850 (the WOTC Pre-screen Notice) for qualifying employees hired in 2014.  The extended deadline for submitting the applications for affected employees is now April 30, 2015.  From the Notice:

Because [Tax Increase Prevention Act of 2014] extended the WOTC retroactively for 2014 for members of targeted groups, employers need additional time to comply with the requirements of § 51(d)(13)(A). Accordingly, a taxable employer that hired a member of a targeted group (as defined in §§ 51(d)(2) through (10)), or a qualified tax-exempt organization that hired a qualified veteran described in § 51(d)(3), on or after January 1, 2014, and before January 1, 2015, will be considered to have satisfied the requirements of § 51(d)(13)(A)(ii) if it submits the completed Form 8850 to the appropriate DLA to request certification not later than April 30, 2015.

A timely request for certification does not eliminate the need for the employer to receive a certification before claiming the credit.

What does this mean in practical terms?

• • Employers who were sitting on the fence in 2014 may now submit WOTC applications for employees hired in 2014.
  • Moreover, employers who were actively screening and submitting WOTC applications during 2014 — but who declined to submit one or more applications because the 28-day deadline had been missed — may now reconsider and submit those “late” applications.
  • All applications for employees hired in 2014 must be submitted on or before April 30, 2015.