If you trawl auction sites for business liquidations, you can also usually pick up an actual rack for pennies on the dollar.

It doesn't even have to be a tech business; most random offices have a small rack in a closet somewhere with some networking equipment on it, and the whole thing usually sells as one lot to anyone with $50 and a screwdriver to remove the equipment from the site.

The tops of the posts are still solid. You could mount a single rack unit and be okay, but fully populating lack legs is not recommended. Cute way to hide a network switch, though.

I have an old Lack (20 years) and while I've never used it as a rack, it'd just been retired from under the TV as I got a new one with a wider base. I notice that even though it's never been moved much, it doesn't feel very stable any more and I wouldn't trust it with a rack of heavy equipment, especially with HDDs that could suffer catastrophic failure if they fell. That said, attaching brackets would sure up the legs a bit. Ideally you'd want to attack brackets at the back as well I guess.

I also had a Billy sat next to it, and did similar to this (but again not racked), with all of my AV gear inside. The door was great, it'd make any status lights diffuse and so they wouldn't interrupt watching a film in the dark (and my old Sky box used to have annoying blue LEDs with an animation when playing back a recorded show), but at the same time remote controls still worked through the glass. Literally best of both worlds. I cut a big hole in the back for cables, which also served well for airflow. I considered adding a fan, but never needed it. I suspect there would be issues with negative pressure doing that though.

I swear every year that passes it sounds more plausible that IKEA has a bunch of people chewing on wood and putting it together into furniture like they were building wasp nests. Their stuff makes frickin' papier-mâché look like a steel girder in comparison.