Why would WB push it to 2020? If it gets pushed back, it will likely move to a summer 2019 spot. If 6 Million Dollar Man doesn't go into production on schedule, I can see WB pushing Shazam to May 31 or August 2, no later than August. I have a feeling WB is keeping that April date because it's a nice cushion between MCU films. If Shazam gets similar buzz and reviews to WW, it has 3-4 weeks to itself before Avengers 4 comes along.
I like it! Light-hearted and tongue-in-cheek, similar to what Marvel did for GOTG.