We will be adding some type of visual indicator for chattability in the future, although perhaps not until LimeWire 1.8, or possibly in LimeWire 1.7c (LimeWire 1.6b is about to be released in beta -- it only has very minor changes to 1.7).

That said, if you really want to see people who you can chat with, try searching for "LimeWire 1.7." People returning results should be 1.7 users. If you right-click on their search result, you should see the chat option. You can also right-click to chat with 1.7 users who you are downloading from or who are uploading from you.