I want to see what it would look like if you put some hue strip lights in the back along the wall. I have hidden Hue lights set to automatically change through out the day to match the color temperature outside. I think you might be able to do an unseen daylight light effect there. Otherwise you could backlight a 3form architectural panel.

That is unusual. Someone was making a design statement.

You could have it wallboarded in with a soffit. Or distract the eye by using brightly colored, interesting things visible from the white kitchen in the living room area.

That is interesting - I would probably wall it in too and paint the vertical ”strips” the same color as the cabinets

I would probably fill it in. But the vertical partitions are there so I don't think I would try to camouflage them or cut them partway off or put crown moulding on them.

This is a contemporary treatment, traditional mouldings are not going to look good with this. If you want to save money to remove the partitions and redo that bank of cabinets, that's one thing, but I wouldn't spend much money of a modest budget trying to turn this into something it's not.

IMO way too much space to fill with crown I think in this case a soffitt added to close the space but are you keeping this space as it is or plannong a renovation down the road. If for right now close that in and wait until you have the budget to do it right The expense will be minimal to close it in and at least when you go to renovate you already know what is in the soffitt.Always a mystery why things are done in a new to you home.