The new Gloria prayer says, "On earth peace to people of good will." The Old Gloria said, "and peace to his people on earth." Are we only praying for non-evildoers? What is the emphasis of this change?

​The phrase you cite from the Gloria, (itself a quote from Luke 2:14), is not about who or what we are praying for. Rather, it is about how God's peace comes to rest upon us, and upon this world. 
 
God's peace is not just a human wish that we can have for others; it is the result of being in conformity to His will and about being reconciled to Him. There can be no true peace where there is a refusal to live according to the vision of his kingdom. 
 
The biblical concept of peace, (shalom), does not simply mean an absence of conflict, it means that there is present in the relationship everything that ought to be there, e.g. justice, love, reciprocity, and truth. 
 
Hence, God's peace can only rest on those who are of "good will". The Greek word from Luke’s Gospel translated here as “good will,” is eudokia, a word which describes one who manifests a desire, and delight, who is disposed and open to the Kingdom of God. 
 
Hence, the new translation is both more accurate in terms of the biblical text, and also more theologically accurate. Peace does not just drop out of heaven, on all people. But rather, it results for those who, by God’s grace, are open and disposed to what he is offering. Peace is the result that accrues to those who, by their good will and openness, accept what God offers.