I don't know that the crowds will be insane, but it will be busy. As mentioned, Spring Break is more of a 6-week season at DLR (starting in mid-March and running through Easter) because some school districts tie their break to Easter while others do not. DLR does appear to be expecting the peak of Spring Break to be that week before Easter because that's when the SoCal and SoCal Select AP blockout is in effect. That being said, if you use FP/Maxpass wisely, get there at rope drop, and have a sense of what you want to do, I think you can still have a great trip.
I don't think waiting until 2020 will make much of a difference, unless you're interested in seeing Star Wars Land. It slated to open this summer, so if you wait until 2020 you'll be able to experience that land. Crowds have just been seeming to get worse and worse each year and Star Wars will probably exacerbate the situation. However, if you wait until Spring of 2020 it will have given them two peak seasons (summer and the holidays) to try and figure out how to handle the crowds.