Lasting a long time=sustainable in my book. I don't know any other definition.
It is certainly not forever if this is what you are getting at. With that, I agree.
When I mentioned "a long time" it means 2 or 3 years. That is not sustainable that is a bubble forming and getting ready to pop when the right time comes. I also mentioned that this is the highest ever amount of margin trading in Bitcoin. How can that can be ever sustainable in your book? In reading your retort, In my book we are close in getting to a stage of mania in the trading cycle.
We've already been in a sustainable uptrend for the latest 1.5 years. Not sure what you're talking about.