For the average reader, likely focused on USA stocks, the big question is this a buying opportunity.
The Pivotal Perspective view is to own what is above pivots and short what is below; and if you are adverse to shorting, then just don't own it, or hedge. Though my focus on the daily SPY is the main USA indexes, there are ample opportunities via ETFs (and futures for the funds and pros) on global stock, bond, commodities, and even the currency markets. So if you were really following this method, you would not be sweating this drop because you'd have shorts in IWM from 12/30-31 or worst case 1/4; longs in TLT from 1/6; shorts in oil from 11/4/2015 (below all pivots from that date), and your choice of shorts in FXI, EEM, RSX, and EWZ as all of these have been below all pivots from various points in November or early December last year. And the most important point, you would have been reducing USA long exposure and/or hedging from 1/4 to 1/7.
Back to the buying question. First of all, my view has been clear: "Bear for real with NDX below its YP at 4373."
That said, there are times, namely August 2015 and summer 2011, when some of the major cash indexes at YS1s have been great buys. The thing with both 2011 and 2015 is that NDX held its YP (in the case of 2015, not one hour closed below) and in 2011 NDX had a 2 day slight break then recovered. Not the case in 2016 - NDX had clear massive rejection of its YP.
So you might pick off a low if buying YS1s, but the easier method is to focus on buying what is above pivots and shorting, hedging or avoiding what is below. This will keep you out of trouble. You might not pick off the exact low, but you'll have far fewer counter-trend trades and a lot less headache. For longer term investors, I would even say you'd want to see something above a quarterly level.
In fact, if you followed this rule of only buying an asset when it is above a quarterly pivot, then you would have had gains or small losses at worst buying oil in 2014-15, gold in 2013-15, and XLF in 2008, and NDX in 2001-02. So perhaps the market will make a mockery of this method this time, but if you can avoid major losses in the worst downtrends and still get back in when the trend changes to up, then that is good enough for me.
For traders, then as I wrote in the SPY daily post yesterday, ES above 1866 and NQ above 4130 could trigger a speculative buy, but whether that gives 1 day bounce or 1 week or is low of the year, who knows. If trying that first I'd want to see an hourly bar with volume close above and then quickly reclaim its weekly pivot. So far only 2 bars in globex have been convincingly above the level with 1866 acting as support, and to my eyes not really decent session bar clearly lifting from 1866. This could change in minutes, and that's the game of trading - you can always get out or get back in.