Define "replaced".
One thing is for sure, Bitcoin currently has the advantage of the brand, everyone's talking about it.
As history has taught us time and time again, the best technology doesn't always win. I'm not saying that Bitcoin is based on poor technology, much the opposite, it's remarkable, but most people just do not care.
Anything that hopes to "replace" Bitcoin any time soon will need much more than some trivial technical improvements. In my opinion even POS might not be enough (and this coming from someone with a small stake in NXT).
This point is most important. The first-to-market advantage is hard to overcome by a competitor. A true replacement would need to be a major improvement over bitcoin, PoS is nice but not nearly enough.