The coinbase article states following regarding the price prediction:

Price response?
It remains unclear whether the upgrade will cause prices to increase or decrease. As mining slows, the price may fall.

However, the upgrades should increase the amount of users on the system overall, causing the price to rise.

Regardless, Metropolis is the penultimate stop on the road map - Serenity, the next upgrade, should produce an increase in stability, causing greater investment and price support.

Source:
https://cointelegraph.com/news/ethereum-announces-metropolis-hard-fork-coming-late-september