Making this a blocker so we resolve it. Should be quick to code if we have consensus, maybe nothing at all to do here.
I'm not too happy with the fact that the new core discovery process has two real gotcha's. The individual core.properties file can define 'name' and 'dataDir'. It seems too easy to either use the same name for two different cores or use the same dataDir, just copy the core.properties file around and fail to edit one them. In large installations this could be a bear to track down.
Straw-man proposal is the we remove support for them both in discovery mode. The name defaults to the directory in which core.properties is found and the data dir is immediately below there.
Currently, there are checks to fail to load either core if either 'name' or 'dataDir' is defined in more than one core. I think the error reporting is weak, you probably have to look in the log file and there should be a way to get this in the admin UI at least.
Maybe the right thing to do is just leave it as-is and emphasize that specifying the dataDir and name is expert level and you have to get it right, but I wanted to get wider exposure to the problem before we push 4.3 out.