See, if ranking systems make the game completely for someone, they need to replay the whole series and enjoy the story and gameplay. However, you seem to be of the mind that rank helps players enjoy getting that objective or fix their playstyle. This is true. A real ranking system that shows skill will help people want to do good and not quit, but it also has to keep account sales and boosting down to a minimum. Halo 4's system so far is that you get XP for winning, completing games, and doing positive actions for yourself. Whether you lose XP for anything or not is unknown. Each rank-up nets you so many SP for buying weapons, armor, AA's, and Packages/Upgrades. The hidden rank seems to be a true thing and it could be a skill rank. However, the talk of hidden rank so far seems only to be rumors, as you said.
Now, Halo 4 is definitely going to put you with similarly skilled players, but whether your skill is tracked or not is unknown. The hidden rank could be a type of in-game BPR system. Meaning that you are ranked based on skill, but only you can see it. AFAIK, only time will tell. I agree this question needs to be answered with a true and definite statement.