World Athletics sets the time standards and the ranking system. Maybe the IOC has certain guidelines for WA to follow, but I don't think the IOC had any part in the wacky 10k qualifications from random Spanish cross country meets for example. Presumably, WA could tweak thier ranking system or or qualifying standard so that the reigning world champion is always a qualified athlete. They may not have the latitude to allow a 4th entrant from a country a la the World Championships, but that's not what we'd be asking for here. Just say that the reigning champ has met the standard. If thier home country has a trials race and wants to send someone else, fine, but they should always be qualified to go.