Do you actually believe high-value comments will commonly go unendorsed? That seems pretty unlikely to me. I'd only worry about comments that aren't all that compelling — and for obvious reasons, I'm not too worried about losing those.
If anything, I expect it to be too easy to get your comments endorsed, just like it's too easy to get dumb comments upvoted right now.
The core problem is that conversations aren't one way highways made of high-value comments.
Sometimes interesting things may come out of silly ones. Or maybe not. If we assume a conversation is also (not only) as a creative process, then mistakes and silliness are simply part of the process to get to something interesting.
Now, don't get me wrong, I'm not advocating the "far west" attitude; I just think that the up/down voting works enough for the purpose.
Introducing an extra layer is going to push people to behave in a certain way (that somebody define, in an extreme way, groupthinking), which may make things more interesting in a certain way, but far less interesting in another.
There was a certain experiment on a certain site where they switched to Facebook comments, and they found that trolling comments were drastically reduced, but the posts started to look to nice and compliant.
Also, very important, the new system replaces a democracy with (more or less) an aristocracy, and I some doubts about this.
I think it's not about how easy it is to be endorsed. The idea of relying on other people to make your comment visible doesn't sound right. I can probably guess, against which type of comments this measure is for and I'm not sure if it's going to be enough. However, there is a Turkish saying which fits to this situation perfectly: "Damp wood, too, will burn alongside the dry", meaning, drastic measures to get rid of the wrong would damage the correct too.
If anything, I expect it to be too easy to get your comments endorsed, just like it's too easy to get dumb comments upvoted right now.