Don't Wait for a New Design
If you aren't in love with the 9.7-inch iPad's design, you'll probably want to find another tablet.
Thus far we haven't heard about a major redesign. Anything is possible, but the 2019 iPad will probably look and feel a lot like the current model.
In other words, you can expect three colors (silver, gold, gray), two models (Wi-Fi only and LTE, don't expect 5G), two storage options, and a thin 7.5 mm design.
You can also expect Apple to keep the Lightning standard around for one more year.
If you're hoping for an edge-to-edge display or another huge design upgrade, it's time to move on and buy/wait for something else.