That's an interesting point. But I can't get if your are talking about the price or the "adoption", i mean: a speculator "adopts" bitcoins iff he buys them once, it doesn't matter if he sells them after.  And that should be S shaped.

Also "hoarding function" should be S shaped, where hoarding means truly belive in long term prospects of bitcoin and do not sell  under a very high price.

We need a model of demand/supply, given this two S shaped extremes. Just thinking loudly.