If the price spikes in December, it will come with a flood of buy/sell orders.  But: remember what happened in Nov when the BTC fork was cancelled?  The BTC blockchain was clogged up for quite a while.  If a spike happens again, buy/sell orders might sit for hours (days?) before 6+ confirmations are generated.  If that sort of processing delay becomes common-place (every time there is a sharp spike in price); it could lead to some erosion of faith in BTC.  Also, with institutional investors coming online soon, that's only going exacerbate the issue (due to increased volume).

My guess is that Core will need to increase the number of transactions/sec that BTC can handle...and that means another fork, probably in 2018.

Thoughts?