If the sports were started today it would make a lot of sense to have orienteering, rogaine, mountain marathons and AR under one umbrella of 'adventure navigation sports' or something like that. Having raced in all of these sports they are essentially the same sports. I hope I haven't offended anyone in saying that but in all of these sports you have a map and a compass and need to get from point A to B to C (almost) any way you want (ie., the same sport). An avid orienteer could argue that mountain marathons are ultra long orienteerig races, Rogaine is 24 hour orienteering and AR is multisport orienteering. Or perhaps an adventure racer would argue that orienteering is adventure running and MTB-O is adventure MTB.
Despite there being so much similarity I doubt this proposal will go anywhere because the sports have developed differently. Orienteering being bigger participation wise internationally and AR being higher profile. Why have the sports developed this way? Orienteering has a very tight set of rules and as such a much higher standard for race fairness, quality (maps, courses, control placement, etc). and for safety. It is easier to attract people from a broader age group. AR has more sponsorship, much higher prizing and perhaps internationally greater links to media but it also has a lot more freedom to explore those areas since the rules are much looser. One could argue that both sports are better for the way they have developed. So I can see why AR would feel they would lose 'spirit of adventure' but also gain a lot by being under IOF.
As an example of losing spirit of adventure, if you look at the maps and courses in early orienteering in Canada it reflects what essentially AR is today in Canada. Then orienteering in Canada moved to the international standards of mapping and course design - eliminating (mostly) the luck element of navigation. Many in orienteering would consider this important while many in AR would consider this against the 'spirit of the sport' as you perhaps develop a slightly different skills set for navigation when those luck elements (new trail, flooded valley) exist. But despite that the sports (I believe) are still essentially the same (map, compass, course, adventure).
Staying with a Canadian context now I honestly believe the two sports must work together much more like is done in other countries. The two sports can (and I would argue need to) learn a lot from each other. The collective expertise of race directors, athletes, coaches, mapping, etc. in the sports is incredible and complementary but each sport on its own does not have that level of expertise to develop and grow. Up to now there has been been too much AR vs. O attitude in Canada (each sport distancing themselves from the other, stating why they are not the other). But lets face it if the two sports were to work together more then the entire 'Adventure Navigation sport' community (athletes, race directors, etc.) in Canada would win.
A step in the right direction is doing what is done in France. If you visit the French Orienteering Federation web site you will see that this is a one-stop link for O, MTB-O, mountain marathons and AR.
http://www.ffco.asso.fr/