I dont think Imran Khan would be able to get 2/3 majority, the political dynamics of Pakistan do not warrant it.
1- We will have to consider how many of the supporters of Imran Khan will be able to cast their vote or more simply, how many are registered voters.
2- The politics landscape is very diverse, While in Upper Punjab the voting depends upon the political leadership i.e. voters vote for party leader.However, the lower Punjab is a complete difference where the candidate matters most.The same situation prevails in Interior Sind and Balochistan as well. In Karachi, most of the voting is based on language basis. Thus In short, the politics in Pakistan depends upon both candidate and leader. Thus at places the leader has to compromise with candidates which deprives any Political leader of leverage over its party and thus the prospect of 2/3 majority, is honestly, a political impossibility for any party.