I understand AI is progressing exponentially but there must be a point where it levels off and gains are not as noticeable until another breakthrough.

Depends in what areas you talking, for example in arts is still growing, slowly but consistent.

An AI echo chamber, I hadn't thought about that🤔

Should we hope that this will be the starting point of its consciousness? However, is it even possible for the training data to run out unless AI would be denied access to it?

yes which is why lightning is necessary to pay humans for training data from here on out

No, because it can still measure response to its output and cyclically feed itself the most positive responses as new training data.

It could eventually be rather self supporting.