Not to come off as a curmudgeon, but what I like about CAKE is that it's Mission Statement is about discussion. I am not a huge cocktail party guy, but, the best parties I have gone to is where I can strike up random, interesting conversations with strangers about a wide variety of topics. At the end of the conversation there would be a mutual respect of shared or not shared ideals and mostly not even a handshake. On to the next conversation. Social media is such a broad landscape where EVERYONE seems to anchor everything in "friendship". I am not looking for any more "friends"; in fact, the older I get, I try and spend my precious time with fewer friends. Not necessarily clones of myself but people I either respect, like or both.
I believe that by NOT having a PM feature, it sort of compells people to basically put their best foot forward and also it disallows any backroom politicking. i.e. "hey George...did you see what Chris implemented on CAKE? WTH was he thinking?" In web terms WYSIWYG.
If at some point you are compelled to add a PM feature, that will not make me pick up my back of toys and leave, but, I just appreciate this is the only "forum" I have ever been a part of that does not have that feature. AND, I LIKE THAT.
In any other forums I turn off all PM features as applicable. ADV is the ONLY forum I allow PM's. There are some crazy cats on ADV, but, something so unique about that culture that having a PM option was important.