On the 1284 you "lose" two of the three interrupts to serial ports which 99% of the time is where you don't want them. On the 32u4 I think you lose them all to serial pins.
The problem I have with that is if you are using those pins for serial you can't use them for unrelated interrupts. If the int pins were elsewhere you could always connect them to a serial pin if you needed that function, but the reverse is not true.
IC that takes HIGH in and outputs GND
I thought they would be great because of the lower pin count, after all you only use about 3 pins on a FT232, but last time I looked the new ones were more expensive.
Rob