i like the idea but i think you have it backwards. i’ll explain:
the loss of players in 1-60 will make the leveling experience for low levels, horrendous, particularly the loss of tanks, cause tanks are gonna roll dks. this means even if blizz gave us RDF, with the nerfing of boosting and the lack of tanks, 1-60 zones are gonna be rough. your idea answers this issue but only half way. rather, consider this:
give 1-70 RDF with a completion bonus better than a booster could give, then remove the nerfs to boosting and level gap. un-nerfing boosts will increase your chances of still getting the run if the RDF doesnt pop, due to lack of tanks but it will more likely to be a free carry or a friendly guildie run since the people boosting for gold and RMT will all be focused on northrend boosts, which they are already on track to do. the boosting nerfs didnt stop the RMT people, but it did stop friends and guildies from helping.