We don't have to wait until blk 2 in anycase.
The main structure to house the radar is the nose. So as long as they are same on all of the production aircraft, AESA can be retrofitted to the older models (with wiring etc) and also to production ones.
The problem is finding the right one. We need a lightweight AESA radar that is not too power hungry. But then we also want it's range to be more than 150Km........why 150?
Because of future longer range BVR AAMs and any potential AWACS killer missile.
Even if we had the EF Typhoon radar, we still wouldn't be able to fit it. So better that PAF issues tender to all the Chinese,European and US firms for AESA radars and gives its specifications.
Much easier to design a plane and put radar in it rather than to make a radar and then design the plane around it!