Certainly, there is a possibility of a decline in price of Bitcoin before or after the halving, but why does JPMORGAN have to caution when he happens to be a holder also. Is he trying to stop investors from making further purchase or he is try to urge everyone to start selling?. The news of a decline in price shouldn't be a problem to those who are long term hodlers, because of the profits ahead.
After this coming halving, there would be a decline in solo mining, as more miners would join a mining pool to combine decent amount of hash power. Number of ASICs, Electricity costs, Maintenance costs and Cooling costs would be a challenging factors to be considered by miners has mining rewards would be reduced and very difficult to mine than the previous.