Not quite the same, but Mike has suggested a similar approach as a backup to finding more 060s and providing an upgrade path for the Replay.
I am looking at an adapter board which will fit in the pins of the 68060 daughter board and carry either a 680x0 or a much faster Virtex7 class FPGA running a soft CPU..
http://www.amiga.org/forums/showpost.php?p=711135&postcount=1863
