Heard of national T20 blast, the England T20 tournament? They don't have many foreign players but still they are getting it right. New Zealand T20 tournament, South African T20 tournament, they do not depend much upon foreign players and still they are getting talent through.
The problem is not foreign players, the problem is quality. In national T20, you get a tournament of I think 16 teams. In super 8 T20 tournament, you have 8 teams with 2 from Karachi and 2 from Lahore. How will a Karachi Blue vs Karachi White match attract people. And add to that, some low level broadcasting quality with Chishti Mujahid and Haroon Rasheed doing commentary in Urdu.
When there will be six teams for a tournament with all this franchise system and hype. You will see houseful in every match and quality will also not be that low as of Super 8 tournament or National T20 tournament.
There is also an outside chance of Afghanistan, Sri Lankan, Windies players agreeing to play in Pakistan.