I think it's awesome. I'd recommend putting a hefty handle on the top on the far side of the opening to initiate the dump process and keep it controlled as you lower it to the garbage can. You'll also do well if you make a curved piece of stiff rubber and attach a handle like a hoe to squeegee the grain off the walls.
Also, don't overlook the plumbing when considering the dumping action. It may seem odd, but attaching the output ball valve to the front of the stand and then connecting it to the tun with silicone tubing would be one way to avoid having to notch out a large portion of the stand.
Thanks! The handle is in the plans and I'm sure will be necessary. The squeegee is a great idea. I had not considered a tubing connection to the bottom. That sounds like it may work out great.