If I have a site that just is not getting listed after 6 months -- is the answer that it will never get listed?
That's not an interesting question. Here's why. Logically, the answer _has_ to be the same to any question of the same form, regardless of the time interval involved.
So, try to imagine a single useful answer that accurately and usefully applies to all three of these questions:
If I have a site that just is not getting listed after 6 milliseconds -- is the answer that it will never get listed?
If I have a site that just is not getting listed after 6 months -- is the answer that it will never get listed?
If I have a site that just is not getting listed after 6 millenia -- is the answer that it will never get listed?
If you don't mind a useful but possibly-false answer, I'd suggest that your suspicion is correct: assume that, indeed, the website won't ever get listed, and make all further decisions based on that assumption. If your assumption is right, your actions will be right. And--if your assumption is wrong, your actions will STILL be right.
Of course, whenever you see yourself in that position, it's also obvious that you're asking perfectly irrelevant questions and making unnecessary assumptions.
Which is one of the reasons we stopped answering questions about when a website might be listed--the answer really wasn't relevant: it really didn't affect any practical decisions.