As a big openbsd aficionado I always wish I could just run bog standard openbsd on my bmc's. ipmi does not do much for me so I would be fine if it were missing a good opensource ipmi stack. Most people would just want to run linux, but the point is, the bmc is just a small computer in charge of monitoring your big computer, however the bmc usually is unable to run an off the shelf operating system, so it is running an old proprietary version of linux with proprietary software. this situation sucks.
An idea I have floating around in the back of my head is to just use a raspberry pi as a bmc on consumer grade hardware, I am sure it would turn out more complicated than this, but basically just hook the power button, i2c, and other headers to the pi's gpio. now you have a bmc that runs an off the shelf os.