Roller blading doesn't seem too niche to me.
Ski touring is a real thing. Skimo is an attempt to distill that into a competitive (and airable) format. It feels like a pretty natural inclusion in the host of alpine & Nordic sports. Much more natural than biathlon.
I'm not sure what the actual inclusion criteria are, but roller blading seems like it might have stiffer competition. Winter sports seem constrained to mostly snow & ice related activities. Summer has to deal with everything else.