Think about this: it took 100 years to have a billion land lines, 1o years to have a billion mobile phones and just one year to have a billion smart phones.
If the FED chooses to let the average maturity of the treasuries it holds shorten, their holdings with maturities between 1 to 5 years should increase a bit, and their holdings with maturities over 1o years should decrease a bit starting in June.