I know Jason Mauck is trying to grow corn and beans together and just harvests them with a regular combine. The tricky part with those is the seed separation, not the harvest.

https://www.youtube.com/watch?v=rN9Kwz45XHo

There are a few of us growing oats and peas together. They are harvested like a normal crop and separated later. I have heard of farmers in Canada doing similar types of mixes with some of their crops: flax, canola, etc.

At this point it’s been more about finding crops that ripen and can be harvested together and cleaned later than creating new equipment. At least on the commercial ag side.