Here's the latest.  It's 6/4 walnut, joined with a maple spline, with some aluminum. Holds you bike with aplomb.

You can see inside the space between the two "U" shaped notches that holds the top tube, there's a rectangle of aluminum.

As for the other two pieces of aluminum, I'd planned on bending it around the wood, but I couldn't get the corners sharp enough without the aluminum snapping. So I mitered the aluminum, and that's (more than) a bit sloppy. It's not a fine metal, stainless steel would have been better (but not without it's own challenges). There's really just too much metal on this, looking at it now. This bike rack was supposed to be about a great piece of walnut, and the aluminum is painfully distracting.

But in my head / on paper / as a model, it seemed so perfect.

Design is an iterative process.

The lip on the front was intended to complement the shape of the opening for the top tube, but it doesn't really do it for me. Makes me think "bird beak", and that wasn't the intention.  The next version will have a simple, gentle, convex curve.

Above you can see the maple spline and a little notch on the top side of the joint. I think without the aluminum, the contrast between the maple and walnut will look much better and the spline would look amazing.
Regarding that notch on the top portion - here's where it gets interesting:

Imaging a whole wall of (non-aluminum-clad) shelves that all interlock, with the bottom lip fitting into the top notch, going up and down and across the wall. Bookshelves, bike racks, and smaller shelves that fit under a bike rack shelf and inside the bike frame. Different widths and depths that allow you to customize your own storage system for your needs, and reconfigure it when you move.

That's all coming down the pike. This basic idea, but it needs to be stripped down.

Let me know what you think.