August the 1st is the planned date for the big "SegWit" update of the Bitcoin algorithm. No one really knows for sure how things will work out. Various effects are in play which might make the whole cryptocurrency market extremely volatile. Most of these effects along with their interplay are probably impossible to predict with any certainty.
There is one effect, though, which seems both strong enough and easy to reason about. I haven't seen this discussed anywhere (admittedly, I might have not searched well enough), so let me post it here, hoping someone here could be interested to offer additional insight or point to a relevant discussion elsewhere.
Consider a typical cryptocurrency exchange along with its typical user, who currently holds some Bitcoins in their account. Although there are multiple views as to how the "SegWit" could affect the future price of Bitcoin, it is probably safe to say that there exists a fair share of "hodlers" - users who strongly believe in the ever raising Bitcoin price and thus will not be selling their Bitcoins anytime soon. Presumably, a considerable proportion of these users also understands the risk of a hard fork with two new Bitcoin chains being born in existence (like it happened with ETH and ETC). Many of these users will hopefully be smart enough to move their Bitcoin from the exchange into a personal wallet (in order to keep hold of their private key and be able to use their coins on both chains, if the split does happen).
Consequently, the supply of Bitcoin on every large exchange should fall noticeably in the upcoming two weeks. As no similar reason exists for moving other altcoins out to offline wallets, their supply will stay more or less the same. Basic microeconomics tells us that in this situation the price of Bitcoin with respect to all other currencies should grow which is equivalent to saying that the price of all altcoins should fall.
Given that most altcoins are traded against Bitcoin, users would probably start seeing red candlesticks on the charts all over, which may add some panic-sellers to the mix, further dropping the prices down.
Anything to add to this logic?
Note that this is not meant to imply any trading advice, nor am I myself involved in cryptocurrency trading to have anything at stake (I'm more into theory). My main interest here is in having a possibility to discuss and later test a specific prediction to see whether "science works, bitches" or perhaps "things are not as simple as they seem" instead.