By the technical definition of a bubble (see https://en.wikipedia.org/wiki/Economic_bubble), I think that bitcoin is probably in bubble territory because there's no good way to figure out what its intrinsic value is.  It also isn't really "backed" by an economic system like fiat currencies.

That said, I'm not really sure how much it matters, at least for the short to medium term.  Ultimately, bitcoin's price will, of course, continue to rise as long as demand exceeds supply.  And there seems to be a lot of potential for increased demand in the form of people who would like to invest but don't have easy access (e.g., through an ETF), as well as skeptics who may eventually decide to board the train (especially large institutions like banks).

Eventually, I think there will be a day of reckoning when the supply of buyers dries up as a result of everyone-who-cares being invested.  However, that day still seems to be a ways off.