Is it possible that we see another altcoin season, if Bitcoin breaches the all-time high and go above 20k? Do you find a direct correlation?
So far this typically was what happened. Times are changing, though, so it's not easy to predict whether alts will see a similar pump as in late 2017. After all, more people are somewhat educated nowadays and chances are they won't be pumping all kinds of shitcoins next time. Otoh, every new ATH brings crypto to the attention of new people, so all kinds of alts may find new fans. Wouldn't surprise me either.
Traditionally, also alts have had higher leverage on an overall market movement (both ways, up and down), which imo is correlated with the fact that most alts are traded mostly against BTC (or ETH, for that matter). Therefore, if they want to buy, let's say, STEEM, they would have to buy BTC with USD first (which would bring the USD/BTC price up), and then the would buy STEEM with BTC, pushing the STEEM / BTC price. This obviously only happens if a lot of people do that, but could explain why we've been seeing that a lot in the past.