If this sudden price rise is due to all of the big, institutional buyers we've been hearing about, bitcoin might not actually be in a bubble.  This might actually be sustainable, but I think it depends on the activity of the short-term traders and/or those who decide to cash out and take their profits.

Bitcoin's at $46.7k as I write this, and it's mind-blowing in the extreme.  It isn't as though it's hit $50k yet, but I didn't think btc would get anywhere near that level this year.  I'm proven wrong once again.