A long-term investor that are selling now are maybe those individuals that must have reach their over accumulation stage whom must have accumulated for over 3-4 cycles or more because I don't think a real Bitcoin investor who has not reached his target will be selling instead of accumulating and HODLing to build up his portfolio for a better future profit which will be a million times better than now, or maybe he/she is selling because of health issues who knows and having no other options but just to sell off their Bitcoin to solve their pressing needs, but even at that selling at once or in large quantity is not a good idea, instead you sell little quantity that will be easily replaceable when the need or time to replace it arise.
Thinking that Bitcoin would still do 1000000X from the current price might seem unrealistic to me. I can agree that Bitcoin would reach unit price of a million dollar or more in coming cycles and that's around only 10x. This multiplier prediction of yours was seen by those very early adopters and I don't think that kind of profits would be seen again. Although Bitcoin promises to be more profitable in the future no doubt, but we need to be more realistic when speculating on it's future price margin.