According to the Teensylu wiki page:
So they are interchangeable. A little more digging and it looks like main difference is that the 1287 supports USB Host mode and not just a device, but that isn't necessary for our normal use.
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Teensylu clone, Atmel's AT90USB1286 - AT90USB1287 drop-in compatible for 20mhz support
So they are interchangeable. A little more digging and it looks like main difference is that the 1287 supports USB Host mode and not just a device, but that isn't necessary for our normal use.