I know it's over a year later, but I've been looking for info for overwintering a huge eggplant plant, and saw your question here. Summer '22 I picked up three 5" Japanese eggplant plants from local Tractor supply store, on sale in 3 or 4" pots, for $4 each. I grew them in central MA, each in a 12 or 14" pot all summer. Got some good yield, and they grew to about 18" high, but I decided to bring them inside for the winter to see if I could get more fruit from them. I put them on a south facing bay window, air temp was never much above 68*, I watered, fertilized once (maybe 2x) from October-May, and hand pollinated flowers with a paint brush. Got about 10 fruits, which I thought was pretty good! Nice and tender and sweet. In late May/early June they went outside, (after hardened off properly) planted 1 into 2' tall raised wooden garden box (with tomatoes, potatoes, basil, borage), 1 into a large deep pot, and one in a conditioned straw bale. The pot one failed, the box and straw bale one thrived and are now 3' tall and maybe 2-3' wide. Tons of flowers, fruit, I couldn't keep up. I'm trying to figure out if I can bring one of them inside again (transplant into v. large pot) and get one more summer out of it! So you can probably grow Ichyban Japanese in your zone, just protect from cooler temps, and bring inside if your season isn't long enough.

- TMR