I did exactly this: installed a panel-ready DW, a Bosch, a year prior to remodeling. The old one died a fantastic and sudden death, and I had to do something.

My Bosch would NOT work without a panel. At all. The door requires at least some amount of weight because the hinge is designed for the extra weight of a panel. (Can't recall at the moment, but it's somewhere between 7 and 12 pounds.)

While you CAN make it work, I strongly recommend against it - if your DW has a hinge like a Bosch, you will end up using far too much force to open the door, and it will slam shut unless you are very careful when you close it. (Don't even think about using the DW when you visit friends or family - I repeatedly slammed their DW doors onto the floor because I was used to the excessive strength required to open my DW before I installed a panel.)

So, yes, either get an inexpensive Ikea panel, or better yet, if you're planning to get custom or even semi-custom cabinets, buy a panel (or have one made) that matches the cabinetry you plan to use in your remodel. Then you can give it a test run.

In my case, I made a temporary custom panel out of scrap from my woodshop (nice scrap, but not first-run lumber), just to make sure the final, "real" panel would look and feel right. My first panel was under the manufacturer-recommended weight limit by about 2 pounds - and I could tell. So when I made the real panel (I made my own cabinets), I designed and constructed it specifically with weight in mind (and of course the outward appearance - because that's why you get panel-ready, right?).