My personal opinion is that it will look just fine as designed. You can't install an under cabinet exhaust without a cabinet as there is nothing to attach it to. If you try to stop it anywhere up the wall, it will cut the vertical line awkwardly. I have a feeling it is a look that you haven't seen in person and it can be hard to visualize.

The hood vent can be built around with framing & drywall, however I think your look will be preferred. Do as teamaltese suggested.

Can you afford another row of cabinets across the ones planned now & carry them clear over the window to the right. Say with one foot high cabinets & have glass doors & LED lights in them?

I do not think you want to add a soffit to terminate the range hood, do you? Is it going to be vented through the ceiling (roof) or could it be terminated somewhare within the height of the wall say at about 8 or 9 feet and vent outside the side wall of the house.

Marie777711 - I don't actually think it will look bad. However, if it really bothers you, I like Sandra's suggestion (if I'm understanding it correctly). You could build out the wall starting at the height of the side wall to the depth of the hood tube. It would also give you the option of a different paint color on the upper wall. It would be a bold, contemporary choice - that may not be your preference.