If we're talking about the weak hands that sold at the bottom of the bear market though, I think they're already FOMOing, since they've demonstrated that their sentiments can be manipulated very easily.
I'm not sure how many of last year's sellers have actually fomo'ed in already. I think that a lot of them paid attention to what the hyperwave squad was saying, therefore people might have believed that sub $2000 levels were due.
Most of the weak hands tend to buy into altcoins, so if we see altcoins lift up harder than Bitcoin, which hasn't really been the case lately, it's safe to say that weak handed retailers aren't fomo'ing yet.
For me to believe that they are blindly buying, altcoins will have to report 10% gains when Bitcoin does 5%, which is how altcoins usually tend to increase. Current rally seems to be driven by smart money rather than dumb money.
i don't think the FOMO is currently from last year's sellers, but i think it is mainly coming from this year's people who were waiting to buy. most of those who sold in 2018, specially in the second half of the year are those wounded newcomers who lost money and are not going to come back any time soon. what we had here were people who were greedy to buy bitcoin as cheap as possible but had their dreams of $1000, etc crushed so they FOMOed right back in to not lose any more.
as for altcoins, they should never be viewed as an investment which entails longer term commitment, but they should instead be viewed as short term tools for pump and dumping to increase the bitcoin wealth of the traders.