I will not think about replacing bitcoin because it will never happen. But increasing the market value, this is more likely. Despite of the recent changes of the market, Ethereum has been performing well and it has reached to $170. The ETHs market was so good lately and you can think of it that it will show a better performance that the recent one but incomparable to the bull run performance.
Thats next to impossible when you compare their market cap and volume. I love ethereum and its one of the best altcoin out there or yet the best. But with such popularity and tech wise? Bitcoin beats them to the ground. POS is a new system and lots of project are into it. But PoW for me still the best mechanism or consensus that works fine. Though, in terms of consumption it really outrun it, but thats not the reason why it is good but the ability to extend scalability on their best. Anyway, if ethereum transfer and migration can be seen successfully we can watch what would be the result but since its not yet happening better to observe first.
PoW is safer and there's also an advantage for PoS and that's making the rich people richer because they can simply invest, buy and let their money work for them. That's the algorithm that lies in PoS and that's why many are waiting for it to happen in Ethereum. But as for bitcoin, PoW makes the network more secure and better. Bitcoin and Ethereum are incomparable and they have their own advantages be it as an investment or preferred coin that's why I've said that I'm not thinking about the replacement because it's been said many times.