people used to run cable through the top tube with no reinforcement all the time. I'm sure there are plenty of bikes like this still out there, but it's going to cause failure on some bikes so I wouldn't do it. Go ask in C&V, I have seen some horror stories posted in there.
The brass piece that Nova sells is just an alternative housing, it's not the same as two cable stops with a free run of cable between them. I don't think anyone is saying it's worse, I'm not sure it's better.