I go on that quest every once in a while, too, but without too much luck.
I haven't ran OpenBSD on the BeagleBone Black, but I imagine it has no graphical output of any kind. I see the X packages but the only on-board devices that are listed as supported are:
BeagleBone, BeagleBone Black
Supported on-board devices:
standard serial port (com)
watchdog controller (omdog)
ethernet controller (cpsw)
GPIO controller (omgpio)
so it boots but it seems a little unlikely that you can do much post-1980s work on it.
I run into various ARM platforms at $work. The platform, as a whole, is probably a step backwards from e.g. PowerPC; it's very relevant today because its power consumption is very hard to beat, and between mobile phones, tablets, IoT and in-car infotainment, this is an important topic. But unless you need something that's super low power, the only thing ARM CPUs have to show for themselves is that they aren't x86. This is more than made up for by the headaches involved into getting stuff that runs on a company's Cortex A7 to run on another company's Cortex A7.
This isn't to say that it's a bad thing. Pre-64-bit ARMs were designed (with the exception of some really old stuff in the 80s) as a platform for appliances, not for computers. They're excellent for designing phones and tablets and smart TVs and whatnot. It's trying to bolt a general-purpose environment on top of them that gives people headaches.