When I first showed up, Ray had the idea that RaR was in the final stage and was only for bugfixing and balancing, not new features. In the end RaR did get some new stuff, but getting Ray's approval was rather difficult.
I don't know the details about Ray's rejection of freeing slaves, but the implementation could easily leave room for abuse. Think civ2. The wonder Leonardo's workshop upgrades obsolete units to the new replacement units for free. One of those upgrades are warriors to musketeers. In other words if you stockpile warriors just before inventing gunpowder, you get musketeers for 10 production each. It kind of feels like an instant army cheat.
Now the biggest problem is: who should look into a fair implementation? RaR development doesn't have the modding manhours that it once did. Personally I'm mainly focused on the xml editor and then Medieval Conquest. While I haven't abandoned RaR, I have had to decide to make it bugfixing only. It's not a dislike for RaR, but rather facing reality and admitting that I don't have unlimited time for modding and can't do every single task that I want to do.