The events already exist for sure (Dakar, Maroc, Safari, Baja, Dos Sertoes, etc), so the biggest issues would be administrative, logistical and not the least commercial. Would the danger of a true world series of rallye be a kind of F1 league of motos due to the sheer cost? The greatest draw of so many rallyes is the grass roots accessibility and drama of it all and to finish as a privateer. No doubt there is nowhere near as much dinero$ available from the major manufacturers to field teams, let alone private sponsors, which really just leaves the energy drink guzzlers. And who knows how long it will be before that bubble bursts, or pops (burp).
Now comes with less dak and more arrgh!