Let's go back to January 2018 which is what a lot of people are comparing this current ramp in the market to. There are huge differences in investor behavior, the media narrative and economic conditions. Back then, high bullishness was clearly evident as indicated by huge equity fund flows, AAII investor sentiment and the general media narrative signing praise of the "global synchronized growth" that was taking place. This time around, despite the market making all time highs day after day for months, public sentiment is only mildly bullish via AAII and agnostic via fund flows (which carry more weight as it tells you what people are actually doing with money). The only extremes out there are in the options market and hedge fund community which are indeed high enough to fuel a correction as they are weak longs and will bail easily. The media is nowhere close to the "blue skies ahead" narrative of January 2018. Although there is less concern about a recession, the media is nowhere close to being optimistic as they were in early 2018 given the global economy continues to be generally stuck in 2nd gear. So, all in all it would appear that when we do get a correction in the market, it will not be as severe as what we saw in 2018. I would speculate that once this ramp in over we could see a long, drawn out consolidation phase whereby the market doesn't suffer more than a 10% drop from the high. That's just my best guess of course. As usual, my expectations can change as things unfold.
A couple of notable things are the weakness in oil and strength in bonds which could be indicating a further softening economy or at the very least one that is still stuck in 2nd gear. If these concerns gather steam it could lead to a correction that has some staying power. As I type this the market appears to be selling off on fears of the conoravirus spreading. If that's the case I don't think such a correction would be long lived.
Bottom line here is that if you're an investor/trader it's a tough spot to be in right now if you have new money to invest. In my opinion the market is too extended to go long but there's not enough extremes to go short in a way that you can do so with conviction. If this dip we are seeing gathers steam I don't think it will last more than a day or 2 if it's due to the coronavirus as this is a weak excuse for a sell off. Given the amount of weak longs out there (hedge funds) though, it could end up being a sharp dip but a short lived one... it's a really tough call at this point.