Wildstein's charge is not a surprise, given his claims (through counsel) virtually since the scandal broke and once New Jersey legislative committees began investigating and holding hearings in late 2013. Those investigations likely begat the federal prosecutors' investigation which led to the indictments of Bill Baroni and Bridget Kelly (who are the ones on trial) and to Wildstein's guilty plea, entered in court on the same day as Baroni and Kelly were arraigned in May 2015.
There is one other question to be raised, and it is less a legal question than a judgment and temperament question. Should the allegations be confirmed, they will make Christie look extraordinarily vindictive and prone to the abuse of power. These qualities will likely impair his attractiveness to an appointed position in a Republican presidential administration. However, they should also raise questions as to his fitness to serve as the United States Attorney, the position he held from 2002 to 2008 (appointed by President George W. Bush).