There are a couple of 555 circuits out there which toggle TE but they all have issues, of one form or another.
The MAX13414 and MAX13487E-MAX13488E have auto direction control.
However you would normally still need to know when the last byte has gone if you are writing a protocol and the auto turnaround doesn't help with that.
using dominant byte collision handling like CanBus but with 485 electrical resilience.
Easy if you wire the transceivers in a non-standard way so the 1 level is hi-z and use fail safe biasing. But you won't get full speed.
using dominant byte collision
If you use byte collision detection it's destructive and you will lose all data being transmitted. Bit level detection can be non-destructive, but that's a lot harder to code and will probably stop the processor from doing anything else when it's transmitting.
It's mostly for these reasons I'm using a ring topology with a dedicated processor for the network. Also I think it's fair to say that a ring is more robust than a net, at the expense of more wires.
EDIT: I think I just thought of a way to make byte-level detection non-destructive, as long as you only have 8 nodes or priority levels.
Rob