Optiloader currently reads the entire bootloader image (512bytes) into RAM (from .hex format in flash.)
This won't be possible with an 8192 byte image. I think this is one of the things that has been improved in the Adafruit version, though. Since there is a worse than 2:1 size difference between hex and binary, it may even be difficult to fit the 8192 byte image in flash (on a 32kbyte part) at all.