First, let me say that RBA can be a misleading term. A true RBA involves removing the coil and/or wick system from your atty and actually making your own coil and wick. This is really a more advanced idea and involves the use and knowledge of an ohm meter, and should only be done if you have a more advanced mod that has short circuit protection.
I think what you are asking about is the tank systems that have been coming out that have "replaceable" heads. There are many brands, kanger, vivi nova, etc... These are great tank systems and have the ability to hold anywhere from 1.5ml to 6ml depending on your personal preferences.
I personally only vape the vivi nova 2.5 tanks right now (when I use a tank). I have found them to be easy to use, produce great vapor, and good flavor. The head is easy to replace, they are easy to refill, and easy to clean. Now, thanks to Phil Busardo at tasteyourjuice.com, I am actually rebuilding my own heads as well.
I hope that this clarifies the idea of replaceable vs. rebuildable and gives you some more information to make a decision that is right for you. Always remember that vaping is a personal experience, and what is right for one vaper isn't always best for you.