As discussed many times before, anything can become a bubble if it grows to big too fast.
Bitcoin had a couple of bubble-like growth periods and will have more; this doesn't make it a scam or ponzi or "a bubble".
Even now, after a way too quick growth, we already have a correction. Nothing unusual. And since you also asked for speculation, I think the Bitcoin will rise big, of course, with corrections now and then.
40-50k is possible in the next 365 days.