IMHO, bitcoin can adopt most of the features that based on bitcoin code, that is for sure.
However bitcoin is too big to make any decision to adapt new changes lightly without causing issues/mass panic.
any changes to bitcoin would affect tons of investors (eg, asic miners, manufacturers).

By the time bitcoin realized certain features (let say primecoin's POW ) is worthy to be implemented, the coin might already gaining too much momentum to be even stopped or slowed by bitcoin.