Using I2C to keep track of position of slaves
This is indeed not possible.  I2C was meant for short on-the-same-board communications and though it's sometimes also extended to near-board communications, it still has no facility for position sensing.  Each slave  simply listens for an address and then responds to commands sent for that address.

Slaves can "stretch the clock" to slow down things, but cannot otherwise make themselves known so long as they are not mastering the bus.  In any case, even if bus mastering is assigned round-robin, only presence can be determined, not the position in any chain.