There could be a $3 trillion shift in investing, and it poses a huge problem for mutual funds

Exchange-traded funds could gain a further $2 trillion to $3 trillion in assets in the next three to five years, according to a report by Morgan Stanley and Oliver Wyman
The rise of ETFs has put pressure on mutual fund fees, forcing many funds to cut costs
In response, mutual funds are expected to invest heavily in ETFs to save money
A dramatic shift is underway in the investment world.
Passive investment products like exchange-traded funds have hoovered up assets at a fast clip in recent years