Actually Cyclocross is gaining in popularity. Those races can be really fun! In Spain there was huge participation, which made it very interesting riding in traffic throughout the course. And the courses can be very spectator-friendly, something unicycling needs more of. I had a blast at the one in Spain, and the one at the USA Nationals in WA in 2017. As for equipment, it depends on the course but so far I’ve seen a mix of Munis and 36ers. I used my 26" Muni, because that’s what I have, which leaves me the option to choose the correct holes for my pedals.
Highwire/slackline could be included in the Entertainment section, even though many people do it for hobby, just as they do with a lot of other performing skills. Probably to include a mix of competition and non-competitive “activities”, you might need to do a chart with overlapping circles or something. You can make them look like wheels…
While most competition events are based on “regular activities”, they tend to get distorted over time, to fit the specific requirements of that competition event. So one possible way to separate things in the chart would be to differentiate competition events from the activities that aren’t competitions, or otherwise the versions of those activities that differ from the competition events. Even then, it will be necessary to note that competition events change and grow over time.
It’s an ambitious endeavor. There will be no perfect way to do it, so remember to have fun with it!